Metal alloy composites

ABSTRACT

This invention relates to metal composites and to metal-alloy composites. Metal-alloy composites of this invention comprise a metal alloy and layered inorganic nanostructures or nanoparticles such as nanotubes, nanoscrolls, spherical or quasi-spherical nanoparticles, nano-platelets or combinations thereof. Methods of producing the metal composites and the metal-alloy composites are demonstrated. The layered inorganic nanostructure serves as a strengthening phase. The layered inorganic nanostructure provides reinforcement to the metal alloy.

FIELD OF THE INVENTION

This invention relates to metal composites and metal-alloy composites. Metal-alloy composites of this invention comprise metal alloy and layered inorganic nanostructures such as nanotubes and spherical nanoparticles. The layered inorganic nanostructures provide reinforcement to the metal alloy. Methods of producing the metal alloy composites are demonstrated.

BACKGROUND OF THE INVENTION

Fuel saving considerations and new technological developments drive metal alloys strongly into the realm of everyday life in the automotive, aerospace, medical technologies and other industries. However, the process engineering of such alloys is often times compromised by their relatively poor mechanical properties.

For example, magnesium (Mg) alloys are gaining more recognition as a lightest structural material for light-weight applications, due to their low density and high stiffness-to-weight ratio. In spite of this, Mg alloys have not been used for critical mechanical applications mainly due to their inferior mechanical properties compared to other engineering materials such as steel and aluminum. Hence, attempts have been made to fabricate Mg-based metal-matrix composites (Mg MMC's) by different methods in order to obtain light-weight Mg MMC's with enhanced mechanical properties.

In recent years, ceramic nanoparticles, such as SiC and Al₂O₃ nanoparticles have been used to reinforce different metallic materials to form metal matrix composites. The proposed mechanisms for the strengthened metal-matrix composites (MMC's) were thermal expansion mismatch, Orowan looping, Hall-Petch relation and the shear-lag model. The thermal expansion mismatch between the nanoparticles and the matrix results in increased dislocation density, increasing thereby the yield strength of the nano-MMC's. The nanoparticles in the matrix can impede dislocation motion during tensile testing. They can also lead to dislocation bowing, and subsequent formation of dislocation loops around the nanoparticle, i.e. the Orowan looping mechanism. Orowan looping mechanism is more pronounced in MMC's reinforced with ceramic nanoparticles of low aspect ratio, i.e. close to unity. According to the Orowan mechanism, finer particles are more efficient in improving the mechanical properties of the composite.

The introduction of nanomaterials into the metal matrix to form composites is rather difficult due to the harsh manufacturing conditions employed for processing the metal composites. The main challenges for processing nano-MMCs are: a. reaching homogeneous dispersion of the reinforcing nanomaterials in the metal matrix; b. the formation of sufficiently strong interfacial bonding; and c. retention of the chemical and structural constancy of the nanomaterials, and in particular preventing its oxidation.

The addition of nanoparticles with high aspect ratio can enhance the mechanical properties of the MMC's without resorting to heavy machining which induce substantial plastic deformation. Thus MMC's can lead also to improved stress corrosion resistance of the Mg-alloys. The stiffening and strengthening effects of such nanofillers depends greatly on achieving effective stress-transfer across the metal matrix-nanofiller interface. The aspect ratio, homogeneous dispersion of nanofillers in the matrix, and the formation of interfacial products also govern the load transfer efficiency of nanomaterials in MMC.

Carbon nanotubes (CNT's) tend to tangle with each other due to the van der Walls force and the mutual interaction through the π electrons, the so-called π-π interaction. Since carbon becomes reactive with numerous metals at elevated temperatures, the structural integrity of CNT's is impaired under high-temperature processing and high pressure conditions. Besides, the chemical reaction between CNTs and the molten metal leads to the formation of interfacial products, like carbides, causing structural damage of the nanomaterials. Synthesizing carbide films, such as Al₂MgC₂ at the interfaces is vital for producing CNTs metal composites having high strength and acceptable ductility. Mg-rich alloy (AZ61) MMC was reinforced by CNTs. The CNTs were first dispersed in isopropyl alcohol (IPA) using zwitterionic surfactant. Spark plasma sintering (SPS) of the MMC produced the Al₂MgC₂ phase at the interface between the CNT agglomerates and the Mg-alloy. The fabricated composite showed increased elongation compared with the pure metal alloy. In another series of experiments, powder metallurgy (PM) was used for the addition of CNTs to AZ61 Mg MMCs. Like the previous study, the nanotubes were dispersed in the AZ61 alloy with the help of an IPA-based zwitterionic surfactant. The yield strength increased by 21.1, 23.4, and 28.5 MPa, respectively, compared with pristine AZ61 (about 225 MPa). Contrarily, water based (CNT) solutions produces substantial amounts of MgO which reduced the ductility of the Mg-alloy. Therefore, employing IPA-based solution could prevent producing excess amount of MgO during the MMCs processing and was beneficial to the mechanical properties of the MMC's.

Powder metallurgy (PM) technique is a versatile process for manufacturing nano-MMC's due to its simplicity, flexibility and net-shape capability. The main drawback of the PM process is the high cost of the raw material powders. The mechanical properties of nano-MMCs, such as hardness and yield strength, can be increased to some extent by PM accompanied by hot extrusion.

Extruded AZ91D Mg MMC's compounded with 1, 3, 5 wt. % CNT's exhibited increased yield strength of 27%, 22.4% and 19.4% compared to that of extruded AZ91D, respectively. However, the ductility of the MMC's deteriorated with increasing content of the CNT's. Hot extruded pure Mg MMC's reinforced by 0.3 and 1.3 wt % CNT's have shown a 1.5% and 11.1% increase in the yield strength compared to that of pure Mg (126 MPa), respectively.

AZ61 nano-MMCs reinforced by 0.5 wt %, 1 wt %, 2 wt % and 4 wt % CNT's which was processed by mechanical ball milling, cold pressing and subsequently hot extrusion (without sintering step), exhibited 27%, 21%, 34% and 34% reduction in the wear rates as compared to the alloy containing no CNT (AZ61). Tribological tests of Mg/micro SiC/MWCNTs MMC's showed better wear resistance than that of monolithic Mg and Mg/micro SiC MMC's under high load of 40 N and high sliding velocity of 3.5 m/s. The main penalty in using such endergonic techniques is that they induce appreciable plastic deformations in the solid and consequently expedite severe stress corrosion.

In view of their potential applications, there is a need to produce stable and robust metal alloy composites with enhanced mechanical properties. There is a need to explore the potential contribution of novel nanostructures to such metal alloy composites.

SUMMARY OF THE INVENTION

In one embodiment, this invention provides a metal alloy composite material improved in mechanical strength as well as elongation and a method for making the same.

In accordance with some embodiments of the present invention, a method for making a metal alloy composite material is provided. The method includes: providing a metal alloy matrix and reinforcement; heating the metal alloy matrix to form a metal solution; adding the reinforcement into the metal solution; cooling down the metal solution containing the reinforcement to form a composite material; and optionally performing a solid solution heat treatment to the composite material. The metal alloy matrix is a magnesium-based alloy or an aluminum-based alloy in one embodiment, and the reinforcement is a sulfur-containing compound in one embodiment.

In accordance with some embodiments of the present invention, a metal alloy composite material is provided. The metal alloy composite material includes a metal alloy matrix and a reinforcement strengthening phase, wherein in some embodiments, the metal alloy matrix is a magnesium-based alloy or an aluminum-based alloy and the strengthening phase is a sulfur-containing compound in some embodiments.

Poor mechanical properties of metal alloys such as Mg alloys are an obstacle to their use in new technologies. In order to address this issue, metal-matrix composites (MMC's) of Mg-alloys have been investigated. In one embodiment, small amounts of inorganic layered nanoparticles such as nanotubes were incorporated into Mg alloys and provided enhanced mechanical properties.

In one embodiment, up to 1 wt % of WS₂ nanotubes were mixed with Mg-alloy (AZ31) using a melt-stirring process at a temperature of above 700° C. The new MMC nano-composites exhibit superior mechanical properties compared with the pristine alloy. Metallographic investigation demonstrated that the average grain size has been reduced in inverse proportion to the added amounts of nanotubes up to 1 wt %. Physical considerations suggest that the main mechanism responsible for the reinforcement effect lies in the mismatch between the thermal expansion coefficients of the metal and the nanotubes. This mismatch induced large density of dislocations in the grain boundaries in the vicinity of the nanotube-matrix interface, which obstruct the crack propagation.

In one embodiment, this invention provides a metal-alloy composite comprising:

-   -   metal alloy; and     -   inorganic layered nanostructured material.

In one embodiment, this invention provides a metal composite comprising:

-   -   a metal; and     -   inorganic layered nanostructured material.

In one embodiment, the metal alloy matrix comprises Mg, Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn, Ag, Au or a combination thereof.

In one embodiment, the base metal in said metal alloy is Mg. In one embodiment, the base metal in said metal alloy is Fe, Cu, Al, Ti, Zn, Ni, Mn.

In one embodiment, the metal alloy comprises one or more secondary metals. In one embodiment, the secondary metal(s) in said metal alloy comprises Zn, Al, Cu, Mg, Mn, Sn, Sb, Ag, Au, Pt, Pd, In, Zr, Ni, Fe, C, Si, Ti, Pb, Be, Y, Ce, Nd, Ca, Os, As, Ba, B, Cr, Co, Ga, Ge, Li, Rh, Ru, Se, Sr, W, Na, Pt, Cd, Bi, Si or a combination thereof.

In one embodiment, the layered inorganic nanostructured material is a spherical or a quasi-spherical nanoparticle, a nanotube, a nanoscroll, a sheet, a distorted sheet, a nanoplatelet or a combination thereof.

In one embodiment, the layered inorganic nanostructured material comprises a sulfur-containing compound.

In one embodiment, the layered inorganic nanostructured material comprises WS₂, MoS₂, or a combination thereof. In one embodiment, the sulfur-containing compound is 2H-phase WS₂.

In one embodiment, the concentration of said layered inorganic nanostructured material in said composite ranges between 0.001 wt % to 15 wt %. In one embodiment, the concentration of the layered inorganic nanostructured material in said composite ranges between 0.001% and 1%.

In one embodiment, the % increase in yield strength of the composite with respect to an alloy without the inorganic layered nanostructure ranges between 15% and 20%. In one embodiment, the % increase in ultimate tensile strength of the composite with respect to an alloy without the inorganic layered nanostructure ranges between 45% and 70%. In one embodiment, the % elongation of the composite with respect to an alloy without the inorganic layered nanostructure ranges between 140% and 400%.

In one embodiment, the size of the grains of the composite ranges between 50 μm-100 μm.

In one embodiment, the fracture toughness of the composite is increased with respect to an alloy without the inorganic layered structure. In one embodiment, the % increase of the fracture toughness of the composite with respect to an alloy without the inorganic layered structure is 272%. In one embodiment, the % increase of the fracture toughness of the composite with respect to an alloy without the inorganic layered structure ranges between 250% and 300%.

In one embodiment, composites of the invention possess enhanced properties with respect to the metal alloy without the inorganic layered nanostructure. In one embodiment, the enhanced property is reduced stress-corrosion.

In one embodiment, this invention provides a method for producing a metal-alloy composite comprising:

-   -   metal alloy; and     -   layered inorganic nanostructures;         wherein the method comprises:     -   a. placing the metal alloy and the inorganic layered         nanostructured material in a crucible;     -   b. heating the metal alloy and the inorganic layered         nanostructured material in the crucible to a first temperature,         forming a melt;     -   c. stirring the melt of the metal alloy and the inorganic         layered nanostructured material in the crucible;     -   d. bringing gas into contact with the melt in the crucible;     -   e. optionally heating the melt in the crucible to a second         temperature;     -   f. optionally heating the melt in the crucible to a third         temperature;     -   g. pouring the melt into a mold;     -   h. cooling the melt, thus forming a solid metal-alloy composite.

In one embodiment, this invention provides a method for producing a metal composite comprising:

-   -   a metal; and     -   layered inorganic nanostructures;         wherein said method comprises:     -   a. placing said metal and said inorganic layered nanostructured         material in a crucible;     -   b. heating said metal and said inorganic layered nanostructured         material in said crucible to a first temperature, forming a         melt;     -   c. stirring said melt of said metal and said inorganic layered         nanostructured material in said crucible;     -   d. bringing gas into contact with said melt in said crucible;     -   e. optionally heating said melt in said crucible to a second         temperature;     -   f. optionally heating said melt in said crucible to a third         temperature;     -   g. pouring said melt into a mold;     -   h. cooling said melt, thus forming a solid metal composite.

In one embodiment, the order of steps b, c, and d or any combination thereof is switched or reversed. In one embodiment, steps b, c, and d or any combination thereof are conducted in parallel, or at least partially overlap in time.

In one embodiment, the first temperature is 380-420° C., the second temperature is 580-620° C. and the third temperature is 680-720° C.

In one embodiment, the first temperature, optionally the second temperature, optionally the third temperature or a combination thereof exceeds 700° C.

In one embodiment, the gas is selected from the group consisting of CO₂, SF₆ or a combination thereof.

In one embodiment, the melt is kept at the first temperature and optionally at the second temperature and optionally at the third temperature for a period of time ranging between 10 min-20 min.

In one embodiment, the heating is conducted in a resistance-heating furnace.

In one embodiment, the stirring is conducted using a stirrer. In one embodiment, the stirrer comprises a vane, a blade, a rod, a screw or a combination thereof.

In one embodiment this invention provides a method for producing a metal-alloy composite comprising:

-   -   metal alloy; and     -   layered inorganic nanostructures;         wherein said method comprises:     -   heating a metal alloy to form a metal solution;     -   adding a layered inorganic nanostructure into the metal         solution;     -   cooling down the metal solution containing the metal alloy and         the layered inorganic nano structures to form a composite         material; and     -   optionally performing a solid solution treatment to the         composite material.

In one embodiment, this invention provides a method for producing a metal composite comprising:

-   -   a metal; and     -   layered inorganic nanostructures;         wherein said method comprises:     -   heating a metal to form a melt;     -   adding a layered inorganic nanostructure into the metal melt;     -   cooling down the metal melt containing the metal and the layered         inorganic nanostructures to form a composite material; and     -   optionally performing a solid solution treatment to the         composite material.

In one embodiment, the metal alloy is a magnesium-based alloy or an aluminum-based alloy. In one embodiment, the layered inorganic nanostructure is a sulfur-containing compound. In one embodiment, the sulfur-containing compound comprises tungsten disulfide (WS₂), molybdenum disulfide (MoS₂) or a combination thereof.

In one embodiment, the method further comprises introducing a protective gas when heating the metal alloy matrix.

In one embodiment, introducing the protective gas comprises introducing helium (He), argon (Ar), nitrogen (N₂), sulfur hexafluoride (SF₆), carbon dioxide (CO₂) or a combination thereof.

In one embodiment, the protective gas introduction is stopped after holding a temperature of between 600° C. and 800° C. for 1 min to 2 hour.

In one embodiment, this invention provides a metal composite or a metal-alloy composite comprising:

-   -   metal or metal alloy; and     -   inorganic layered nanostructured material;     -   wherein the metal composite or the metal-alloy composite is         produced by any of the methods described herein above.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which:

FIGS. 1A-1B. FIG. 1A shows SEM image of an assortment of WS₂ nanotubes; FIG. 1B shows TEM image of a single WS₂ nanotube, scale bar is 5 nm.

FIGS. 2A-2C. FIG. 2A shows Schematic rendering of the reactor used for the fabrication of the Mg-MMC with different concentrations of the WS₂ nanotubes; FIG. 2B shows The stainless steel mold used for melting the Mg-alloy and mixing with the WS₂ nanotubes; FIG. 2C shows Optical micrographs of four of the Mg-MMC ingots prepared at different temperatures for an embodiment of the present study. From right to left: 650° C.; 680° C.; 700° C. and 750° C. One notices that the ingots prepared below 700° C. do not appear to be uniform.

FIG. 3 is a plot showing XRD patterns of the AZ31INT0.5-1 sample and a pristine Mg alloy.

FIG. 4 is Stress-strain curve (tensile test) of the pure Mg-AZ31 alloy and the Mg MMC with 1 wt % nanotubes (AZ31INT1−x; x=1−3). Notwithstanding the variation in the results, the Mg-MMC with 1 wt % nanotubes exhibit appreciable improvements in the mechanical properties compared with the pristine alloy.

FIG. 5 is a summary of the mechanical testing of the different Mg-alloy samples.

FIG. 6 shows metallography of the pure Mg alloy and the different Mg alloys formulated with 1 wt % INT-WS₂.

FIGS. 7A-7B. FIG. 7A shows Comparison between the grain sizes, as concluded from the metallographic analysis, for the pristine AZ31 Mg alloy and for different samples of the Mg MMC with 1 wt % INT-WS₂. Note that the grain sizes of the different MMC's are quite similar. Error bars for the results of the analysis are included as well; FIG. 7B shows Comparison between the grain sizes of the pristine AZ31 Mg alloy and the MMC's with 0.5 and 1 wt % of WS₂ nanotubes. The different sizes of the error bars represent the statistical variation of the grain sizes in the analyzed samples. Note that the error bars are diminishing with the addition of larger amounts of the nanotubes.

FIG. 8 illustrates an exemplary flow chart of a method for making a metal alloy composite material.

FIG. 9 illustrates an exemplary cross-sectional view of a furnace for making a metal alloy composite material.

FIGS. 10A through 10C illustrate x-ray diffraction patterns of metal alloy composite materials.

FIGS. 11A through 11C illustrate x-ray diffraction patterns of metal alloy composite materials.

FIGS. 12A through 12F illustrate metallographic photos of metal alloy composite materials.

FIGS. 13A through 13F illustrate metallographic photos of metal alloy composite materials.

It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention.

Introducing nanotubes into molten alloys at high temperatures is extremely challenging and has not been attempted before. The success of such process depends on issues of reactivity of the metal with components of the nanotubes, e.g. sulfides. Accordingly, it was not predicted that metal alloys could be reinforced by e.g. WS₂ or other nanotubes. Therefore, incorporating inorganic nanotubes (e.g. WS₂) in metal-alloys was not previously attempted.

In one embodiment, this invention demonstrates the successful incorporation of inorganic nanotubes into metal alloys. It is shown that WS₂ nanotubes are highly beneficial for improving the mechanical properties of the Mg alloys. For comparison, carbon nanotubes were used but did not exhibit satisfactory results when added to the metal alloys.

In one embodiment, metal alloy composites of this invention are produced by stir casting. In one embodiment, stir-casting methods of this invention are modified to be compatible with small-volume molds. In one embodiment, molds used for the preparation of the present composites is designed to comprise about 200 g of melt and is different from previously used molds comprising about 2000 g of melt.

In one embodiment, the novel composites of this invention comprise a combination of WS₂ nanotubes and Mg alloy. In one embodiment, the novel composites of this invention comprise very small amounts (up to 1%) of nanotubes in a metal-alloy. Although very small amount of nanotubes are incorporated in the alloys, significant improvements in both the stiffness and ductility of the alloy is demonstrated, leading to surprisingly high fracture toughness of the metal matrix composites.

In one embodiment, the high temperature (>700° C.) melt stirring process leads to the significant improvements in stiffness and ductility, and to the surprisingly high fracture toughness of the composite.

Nanoparticles of inorganic layered compounds, like WS₂, MoS₂ and numerous others, fold into tubular particles (inorganic nanotube, INT) and into quasi-spherical inorganic fullerene-like (IF) structures (spherical or quasi-spherical nanoparticles). When added in small amounts to lubricating fluids, these nanoparticles were shown to endow superior tribological behavior to a variety of fluid lubricants.

The enhanced tribological properties of the IF nanoparticles were attributed to their high strength and impact resistance as well as to their ability to roll and their gradual exfoliation and formation of a protective layer on the matting surfaces. Following extensive studies, industrial grade IF-WS₂ nanoparticles were successfully commercialized, primarily for use as additives to high-performance lubricants and greases (“NanoLub”) and also in surface protective polymer films.

In addition, the recent successful synthesis of pure WS₂ nanotubes (INT-WS₂) powder paved the way for numerous studies offering them numerous other applications. FIG. 1A shows a scanning electron microscope (SEM) micrograph of an assortment of WS₂ nanotubes, while FIG. 1B displays a transmission electron microscope (TEM) image of one such multiwall nanotube. The high degree of crystalline perfectness of the nanotube can be appreciated from these figures. This is also reflected by the excellent mechanical properties of such nanotubes. Additionally, the absence of major defects in the crystalline structure of the nanotubes could promote their relative high-temperature stability and impede their oxidation during a melt-stirring process of the MMC.

The application of nanoparticles for improving the tribological properties of polymer composites has been previously demonstrated. However, the processing temperature of such composites does not exceed 350° C. Such temperature range does not jeopardize the thermal stability of the nanoparticles.

Preparation of metallic composites involves appreciably higher processing temperatures. Furthermore, molten metals are known to be very reactive with respect to sulfur and its compounds at high temperatures. This fact was expected to impair the properties of metal-matrix composites comprising nano structures.

In one embodiment, this invention provides the first bulk metal composite reinforced with WS₂ nanotubes. The strengthening mechanisms of these composites are discussed. For comparison, multiwall carbon nanotubes (CNT)-Mg-alloy MMC's were also prepared in this series of experiments. Noticeably, they did not produce any reinforcement effect in this case (see Table 1).

The novel INT-WS₂-based Mg composites of this invention, were prepared by melt-stirring with no further mechanical or chemical processing. These novel INT-WS₂-based Mg composites revealed stronger and tougher properties compared with the pure Mg alloy. This kind of behavior cannot be found in traditional Mg alloys or in Mg composites reinforced by non-layered nanoparticles. Usually, improving the tensile strength of a given material by processing or by adding nanoparticles leads to deterioration of the strain, and vice versa. Improving both strain and strength by severe plastic deformation has been demonstrated. However, such alloys suffered from stress corrosion and exhibited low performance. Surprisingly, the present new Mg composites exhibit both increased tensile strength and elongation (strain) simultaneously. Thus, one of the main goals of this study is to produce new Mg nano-MMCs with superior strength and strain. Such new Mg nano-MMCs could be implemented in the 4C industry (Computer, Communications, Consumer Electronics and Car) and could be used for the aerospace industry and other industries as well.

Composites of the Invention

In one embodiment, this invention provides a metal-alloy composite comprising:

-   -   metal alloy; and     -   inorganic layered nanostructured material.

In one embodiment, this invention provides a metal composite comprising:

-   -   a metal; and     -   inorganic layered nanostructured material.

In one embodiment, the metal alloy comprises Mg, Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn, Ag, Au or a combination thereof. In one embodiment, the base metal in said metal alloy is Fe, Cu, Al, Ti, Zn, Ni, Hg. In one embodiment, the base metal in the metal alloy is Mg.

In one embodiment, the metal alloy comprises one or more secondary metals. In one embodiment, the secondary metal(s) in the metal alloy is Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn or a combination thereof. In one embodiment, the secondary metal(s) in the metal alloy is Al, Zn, Mn or a combination thereof.

In one embodiment, the secondary metal(s) (or semi metals) in said metal alloy is selected from the group consisting of Zn, Al, Cu, Mg, Mn, Sn, Sb, Ag, Au, Pt, Pd, In, Zr, Ni Fe, C, Si, Ti, Pb, Be, Y, Ce, Nd, Ca, Os, As, Ba, B, Cr, Co, Ga, Ge, Li, Rh, Ru, Se, Sr, W, Na, Pt, Cd, Bi, or a combination thereof. In one embodiment, the secondary metal is the alloying element of the alloy.

In one embodiment, the metal alloy further comprises metal impurities. In one embodiment, the metal impurities comprise one or more metals at a wt % of not more than 0.001%, or of not more than 0.01%, or of not more than 0.1%, or of not more than 1% for each metal impurity. In one embodiment, impurities at below 1% are added to metal alloys of this invention to enhance a certain property, such as chemical inertness or a mechanical property. In one embodiment, the impurity materials are selected from metals, metalloids, semi-metals, non-metals or a combination thereof. In one embodiment, impurities such as Zn, Al, Cu, Mg, Mn, Sn, Sb, Ag, Au, Pt, Pd, In, Zr, Ni Fe, C, Si, Ti, Pb, Be, Y, Ce, Nd, Ca, Os, As, Ba, B, Cr, Co, Ga, Ge, Li, Rh, Ru, Se, Sr, W, Na, Pt, Cd, Bi, Si or combinations thereof are added to metal alloys of this invention. In one embodiment, the impurities comprise Si, Fe, Cu, Mn, Zn, Al or a combination thereof.

In another embodiment, there is no distinction between secondary metal and impurity. According to this aspect and in one embodiment, all impurities in metal alloys of this invention are regarded as secondary metals.

In another embodiment, impurities are materials that were not intentionally added to the alloy or to the layered nanostructure or to the composite, but nevertheless are found in the metal alloy/composite in percentages smaller than 1% or smaller than 0.1% or smaller than 0.01% or smaller than 0.001%. According to this aspect and in one embodiment, such impurities do not affect the properties of the metal alloy composite. Accordingly and in one embodiment, metal alloys of this invention comprise impurities which were unintentionally added. In one embodiment, the source of such impurities is in the raw materials used, in materials used in the process (e.g. gases), materials from the process environment, materials from process components (e.g. crucible and hoses), or a combination thereof.

In one embodiment, the inorganic layered nanostructured material comprises a spherical or a quasi-spherical nanoparticle, a nanotube, a nanoscroll, a sheet, a distorted sheet, a nano-platelet or a combination thereof.

In one embodiment, the inorganic layered nanostructured material does not comprise carbon. In one embodiment, the inorganic layered nanostructured material does not comprise carbon nanotubes or carbon fullerenes or carbon fullerene-like (nested-multiwall polyhedral carbon) nanoparticles.

In other embodiments, the inorganic layered nanostructured material comprises both carbon layered nanostructured material and other non-carbon layered inorganic nanostructured material. In one embodiment, the inorganic layered nanostructured material comprises carbon nanotubes, carbon fullerenes, carbon fullerene-like nanoparticles, graphene nano-platelets or a combination thereof.

In one embodiment, the layered inorganic nanostructured material comprises WS₂, MoS₂, or a combination thereof.

In one embodiment, the sulfur-containing compound is 2H-phase WS₂. In one embodiment, the layered inorganic nanostructured material comprises any non-carbon, inorganic layered nanomaterial.

In one embodiment, the concentration of the layered inorganic nanostructured material in the composite ranges between 0.001 wt % to 15 wt %. In one embodiment, the concentration of the layered inorganic nanostructured material in the composite ranges between 0.001 wt % and 1 wt %.

In one embodiment, the concentration of the layered inorganic nanostructured material in the composite ranges between 0.001% and 1%. In one embodiment, the concentration of the layered inorganic nanostructured material in the composite ranges between 0.0001% and 1% or between 0.01% and 1% or between 0.1% and 1% or between 0.001% and 5% or between 0.01% and 2% or between 0.001% and 10% or between 0.0001% and 15% or between 0.1% and 7.5% or between 0.1% and 20% or between 0.001% and 0.1% or between 0.0001% and 0.01% or between 0.0001% and 0.1%. In one embodiment, the concentration of the layered inorganic nanostructured material in the composite is less than 1%. In other embodiments, the concentration of the layered inorganic nanostructured material in the composite is less than 10%. In some embodiments, the concentration is less than 5%. In some embodiments, the concentration is less than 0.1%.

In one embodiment, there is an increase in fracture toughness of the composite with respect to an alloy without the inorganic layered nanostructure. In one embodiment, the % increase in fracture toughness of the composite with respect to an alloy without the inorganic layered structure ranges between 15% and 20%. In one embodiment, the % increase in fracture toughness of the composite with respect to an alloy without the inorganic layered structure ranges between 20% and 50%. In some embodiments, the % increase in fracture toughness ranges between 10% and 50%, between 10% and 100%, between 25% and 75%, between 50% and 150%, between 5% and 100%, between 10% and 300%. In some embodiments, the % increase in fracture toughness ranges between 10% and 200%, between 100% and 300%, between 250% and 300%, between 25% and 250%. In some embodiments, the % increase in fracture toughness is up to 272%. In some embodiments, the % increase in fracture toughness is up to 400%.

In one embodiment, there is an increase in yield strength of the composite with respect to an alloy without the inorganic layered structure. In one embodiment, the % increase in yield strength of the composite with respect to an alloy without the inorganic layered structure ranges between 15% and 20%. In one embodiment, the % increase in yield strength of the composite with respect to an alloy without the inorganic layered structure ranges between 20% and 50%. In some embodiments, the % increase in yield strength ranges between 10% and 50%, between 10% and 100%, between 25% and 75%, between 50% and 150%, between 5% and 100%, between 10% and 75%. In some embodiments, the % increase in yield strength ranges between 10% and 200%, between 100% and 200%, between 25% and 250%. In some embodiments, the % increase in yield strength is up to 200%.

In one embodiment, there is an increase in ultimate tensile strength of the composite with respect to an alloy without the inorganic layered structure. In one embodiment, the % increase in ultimate tensile strength of the composite with respect to an alloy without the inorganic layered structure ranges between 45% and 70%. In one embodiment, the % increase in ultimate tensile strength of the composite with respect to an alloy without the inorganic layered nanostructure ranges between 25% and 75%. In some embodiments, the % increase in ultimate tensile strength ranges between 10% and 100%, between 40% and 60%, between 10% and 150%, between 50% and 150%, between 5% and 100%, between 10% and 75%. In some embodiments, the % increase in ultimate tensile strength ranges between 10% and 200%, between 100% and 200%, between 25% and 250%. In some embodiments, the % increase in ultimate tensile strength is up to 200%.

In one embodiment, there is an increase in elongation of the composite with respect to an alloy without the inorganic layered nanostructure. In one embodiment, the % increase of elongation of the composite with respect to an alloy without the inorganic layered structure ranges between 140% and 400%. In one embodiment, the % increase of elongation of the composite with respect to an alloy without the inorganic layered structure ranges between 100% and 500%. In some embodiments, the % increase of elongation ranges between 200% and 600%, between 50% and 250%, between 100% and 1000%, between 50% and 750%, between 5% and 1000%, between 50% and 500%. In some embodiments, the % increase of elongation ranges between 200% and 800%, between 50% and 800%, between 10% and 800%. In some embodiments, the % increase of elongation is up to 800%.

In one embodiment, the grain size of metal-alloy composites of this invention is smaller than the grain size of the corresponding alloy without the inorganic layered structure. In one embodiment, the size of the grains of the composite ranges between 50 μm-100 μm. In one embodiment, the size of the grains of the composite ranges between 10 μm-200 μm. In some embodiments, the grain size of metal-alloy composites of this invention ranges between 1 μm-100 μm, between 0.5 μm-250 μm, between 25 μm-75 μm, between 10 μm-100 μm, between 50 μm-200 μm, between 50 μm and 500 μm. In some embodiments, the grain size of metal-alloy composites of this invention ranges between 100 μm-500 μm, between 400 μm-600 μm, between 10 μm-500 μm, between 1-600 μm.

Methods of Producing Composites of the Invention

In one embodiment, this invention provides a method for producing a metal-alloy composite comprising:

-   -   metal alloy; and     -   layered inorganic nanostructures;         wherein the method comprises:     -   a. placing the metal alloy and the inorganic layered         nanostructured material in a crucible;     -   b. heating the metal alloy and the inorganic layered         nanostructured material in the crucible to a first temperature,         thus forming a melt;     -   c. stifling the melt of the metal alloy and the inorganic         layered nanostructured material in the crucible;     -   d. bringing gas into contact with the melt in the crucible;     -   e. optionally heating the melt in the crucible to a second         temperature;     -   f. optionally heating the melt in the crucible to a third         temperature;     -   g. pouring the melt into a mold;     -   h. cooling the melt, thus forming a solid metal-alloy composite.

In one embodiment, this invention provides a method for producing a metal composite comprising:

-   -   a metal; and     -   layered inorganic nanostructures;         wherein said method comprises:     -   a. placing said metal and said inorganic layered nanostructured         material in a crucible;     -   b. heating said metal and said inorganic layered nanostructured         material in said crucible to a first temperature, forming a         melt;     -   c. stirring said melt of said metal and said inorganic layered         nanostructured material in said crucible;     -   d. bringing gas into contact with said melt in said crucible;     -   e. optionally heating said melt in said crucible to a second         temperature;     -   f. optionally heating said melt in said crucible to a third         temperature;     -   g. pouring said melt into a mold;     -   h. cooling said melt, thus forming a solid metal composite.

In one embodiment, the order of steps b, c, d or any combination thereof is switched or reversed. In one embodiment, steps b, c, d or any combination thereof are conducted in parallel or at least partially overlap in time.

In one embodiment, the first temperature is 380-420° C., said second temperature is 580-620° C. and said third temperature is 680-720° C.

In one embodiment, the first temperature ranges between 200-700° C. In one embodiment, the first temperature ranges between 500-700° C. In one embodiment, the first temperature ranges between 600-700° C., between 700-800° C., between 700-900° C., between 750-850° C., between 700-1000° C., between 1000-1300° C., between 1200-1500° C. In one embodiment, the first temperature is up to 1000° C. In one embodiment, the first temperature is up to 1300° C. In one embodiment, the first temperature is up to 1500° C. In one embodiment, the first temperature ranges between 300-500° C. or between 300-700° C. In some embodiments, the first temperature is 400±25° C., 450±25° C., 500±25° C., 550±25° C., 600±25° C., 650±25° C., 700±25° C., 700-730° C., 750±25° C., 800±25° C., 850±25° C., 900±25° C., 950±25° C., 1000±25° C., 1050±25° C., 1100±25° C., 1150±25° C., 1200±25° C., 1250±25° C., 1300±25° C. 1350±25° C., 1400±25° C., 1450±25° C., 1500±25° C.

In one embodiment, heating to the first temperature is conducted during a period of a few minutes. In one embodiment, heating to the first temperature is conducted during a period ranging between 10 minutes and 60 min.

In one embodiment, heating to the first temperature is conducted during a period of a few hours. In one embodiment, heating to the first temperature is conducted during a period of 1-3 hours. In one embodiment, heating to the first temperature is conducted during a period of 20 min to 3 hours, or 10 min to 3 hours, or 1-4 hours, or 1-5 hours, or 0.5-2 hours, or 0.5-4 hours. Heating to the first temperature is the time it takes to heat until reaching the first temperature.

In some embodiments, the crucible, and/or the materials in the crucible (or in any other vessel) are kept at the first temperature for a period of time of 10 min-1 hr. In some embodiments, the crucible, and/or the materials in the crucible (or in any other vessel) are kept at the first temperature for a period of time of 1 min-5 hr. In some embodiments, the crucible, and/or the materials in the crucible (or in any other vessel used) are kept at the first temperature for a period of time of 5 min-50 min, or for 10 min-2 hr, or for 0.5 hr-2.5 hr, or for 1 min-10 min, or for 10 min-10 hr, or for 1 hr-3 hr.

In one embodiment, the time required to heat the sample from the first temperature to the second temperature and/or from the second temperature to the third temperature is at the same ranges described herein above for the time required to heat the sample to the first temperature.

In one embodiment, the time the sample is kept at the second temperature and/or at the third temperature is within the same ranges described herein above for the time the sample is kept at the first temperature.

Any other time ranges and temperature ranges are applicable to methods and systems of this invention, depending on parameters of the system, of the materials used, the mass/volume of the alloy used, the power of the furnace etc. as is known to any person of ordinary skill in the art.

In one embodiment, where the method further comprises heating to a second and optionally to a third temperature (optional steps e and f), the second temperature is higher than the first temperature and the third temperature is higher than the second temperature. In one embodiment, where the method further comprises heating to a second and optionally to a third temperature, the second and third temperatures are at any suitable range. In one embodiment, the first temperature ranges between 300 and 500° C., the second temperature ranges between 500 and 700° C. and the third temperature ranges between 600 and 800° C.

In one embodiment, the second temperature and the third temperatures range between 300 and 1000° C.

In one embodiment, gas is brought into contact with the melt in the crucible. In embodiments wherein the gas is introduced to the system before the heating step is performed, the gas is brought into contact with the solids in the crucible.

The gas introduced into the system is the gas that is brought into contact with the melt or with the mixture of solids in the crucible as shown in FIG. 2A. In one embodiment, the gas introduced in to the system is selected from the group consisting of CO₂, SF₆, N₂, Ar or a combination thereof. In one embodiment, any gas or any gas mixture that does not interfere with, or deteriorate or prevents the formation of the novel metal alloy composites of this invention can be used in embodiments of this invention.

In one embodiment, the melt is kept at the first temperature and optionally at the second temperature and optionally at the third temperature for a period of time ranging between 10 min-20 min. In one embodiment, the melt is kept at the first temperature and optionally at the second temperature and optionally at the third temperature for a period of time ranging between 1 min-50 min. In one embodiment, the melt is kept at the first temperature and optionally at the second temperature and optionally at the third temperature for a period of time ranging between 5 min-25 min, or between 1 min-100 min, or between 0.5 min-30 min, or between 12.5 min-17.5 min, or between 10 min-200 min, or between 0.1 min-50 min.

In one embodiment, heating is conducted in a resistance-heating furnace. In one embodiment, heating is conducted in any furnace or oven or vessel that can reach the temperature(s) needed for methods of this invention. In one embodiment, heating comprises solar heating.

In one embodiment, the stirring is conducted using a stirrer. In one embodiment, the stirrer comprising a vane, a blade, a rod, a screw or a combination thereof. In another embodiment, no stirring is conducted in methods of this invention.

In other embodiments, gas stirring is used. Gas stirring is conducted using N₂ or Ar in some embodiments. In some embodiments, a combination of stirring methods is used.

In one embodiment, instead of a crucible, any other suitable vessel may be used. An ampoule, a solid substrate, a powdered substrate, a mold, a vessel, a cylinder, or any other device can be used. The crucible or any other appropriate vessel may be made from any material that can hold the metal alloy and the inorganic layered structures and that can sustain the temperatures applied in methods of this invention. In one embodiment, the crucible or any other vessel or device is inert to the metal-alloy and the inorganic layered structures at the temperatures used in methods of this invention.

In one embodiment, this invention provides a method for producing a metal-alloy composite comprising:

-   -   metal alloy; and     -   layered inorganic nanostructures;         wherein said method comprises:     -   heating a metal alloy to form a metal solution;     -   adding a layered inorganic nanostructure into the metal         solution;     -   cooling down the metal solution containing the metal alloy and         the layered inorganic nanostructures to form a composite         material; and     -   optionally performing a solid solution treatment to the         composite material.

In one embodiment, this invention provides a method for producing a metal composite comprising:

-   -   a metal; and     -   layered inorganic nanostructures;         wherein said method comprises:     -   heating a metal to form a melt;     -   adding a layered inorganic nanostructure into the metal melt;     -   cooling down the metal melt containing the metal and the layered         inorganic nanostructures to form a composite material; and     -   optionally performing a solid solution treatment to the         composite material.

In one embodiment, the metal alloy is a magnesium-based alloy or an aluminum-based alloy. In one embodiment, the layered inorganic nanostructure is a sulfur-containing compound. In one embodiment, the sulfur-containing compound comprises tungsten disulfide (WS₂), molybdenum disulfide (MoS₂) or a combination thereof. In one embodiment, the method further comprises introducing a protective gas when heating the metal or the metal alloy.

In one embodiment, introduction of the protective gas comprises introducing helium (He), argon (Ar), nitrogen (N₂), sulfur hexafluoride (SF₆), carbon dioxide (CO₂) or a combination thereof. In one embodiment, the protective gas introduction is stopped after holding a temperature of between 600° C. and 800° C. for 1 min to 2 hour.

In one embodiment, this invention provides a metal or a metal-alloy composite comprising:

-   -   metal or metal alloy; and     -   inorganic layered nanostructured material;     -   wherein the metal composite or the metal-alloy composite is         produced by any of the methods described herein above.

As will be further described in the examples herein below, small amounts of up to 1 wt % of WS₂ nanotubes (INT-WS₂) were added to the AZ31 Mg-alloy using a melt-stirring reactor operated at 700-730° C. Notwithstanding partial oxidation, the nanotubes showed quite a remarkable stability at these elevated processing temperature and were distributed quite uniformly in the processed ingot. Despite the small amounts of added INT-WS₂, their addition led to remarkable improvements in the mechanical properties of the alloys. Surprisingly, both the tensile strength of the AZ31 alloy and its elongation (and consequently the fracture toughness) were greatly improved.

Metallographic analysis of the alloys clearly showed that the thermal mismatch between the nanotubes and the Mg-alloy leads to the formation of numerous dislocations in the grain boundaries in the vicinity of the nanotube-matrix interface. These dislocations impede the progress of the crack under load.

Contrarily, carbon nanotubes which were added to the same alloy using the melt-stirring technique (see Table 1), did not show any favorable effect on the mechanical properties of such alloys.

TABLE 1 Summary of mechanical measurements of Mg-MMC's, mechanical properties of present nanocomposites and other nanocomposites. Ultimate tensile Yield strength, strength [MPa] [MPa] Elongation Notation Specification (% change) (% change) (% change) AZ31 ^(a)) As-cast AZ31 Mg 84.3 (0) 136.0 (0) 5.3% (0) alloy AZ31INT0.5 ^(a)) AZ31 with 0.5 wt. % 101.1 (+20.0) 203.0 (+49.3) 12.7% (+139.6) WS₂ nanotubes AZ31INT1 ^(a)) AZ31 with 1 wt. % 99.0 (+17.4) 227.7 (+67.4) 25.1% (+373.6) WS₂ nanotubes AZ31CNT0.1 ^(e)) AZ31 with 0.1 wt. % 62.5 (−25.6) 104.8 (−22.9) 3.25% (−38.7) CNT AZ31CNT0.5 ^(e)) AZ31 with 0.5 wt. % 64.0 (−24.1) 114.4 (−15.9) 4.73% (−10.8) CNT Pure Mg ^(b)) Pure Mg 47 ± 3 (0) 120 ± 4 (0) 12.3 ± 1.1% (0) Mg-1 wt % SiC ^(b)) Pure Mg with 1 wt. % 67 ± 4 (+42.0) 133 ± 5 (+10.8) 6.3 ± 0.8% (−48.8) SiC nanoparticles AZ91 ^(c)) As-cast AZ91 Mg 250 (0%) 350 (0%) 16.5% (0%) alloy AZ91MWCNT0.1 ^(c)) AZ91 with 0.1 wt. % 300 (+20.0) 415 (+18.6) 24.5% (+48.5) CNT AZ91 ^(d)) As-cast AZ91 Mg alloy 135 (0) 210 (0) 6% (0) AZ91MWCNT0.1 ^(d)) AZ91 with 0.7 wt. % 210 (+55) 305 (+45) 9% (+50) CNT + 0.3 wt. % SiC ^(a)) Present work: AZ31 and WS₂ nanotubes-AZ31 nanocomposite; ^(b)) literature ^(c)) literature; ^(d)) literature; ^(e)) Present work: CNT AZ31 nanocomposite; ( ) Brackets indicate % change with respect to the corresponding monolithic alloy.

Theory:

Several mechanisms have been offered to explain the reinforcement effect of nanoparticles in different crystalline matrices. Primarily, the Hall-Petch mechanism, which relates the grain size to the fracture toughness of the matrix could be anticipated. More careful analysis for the contribution of each of the four reinforcement mechanisms discussed above was carried-out. Unfortunately, only nanoparticles with isotropic spherical shape could be used in for these calculations. A representative example for such calculations with the different models and parameters used are presented in Table 2.

TABLE 2 Calculated contributions of the different mechanisms for the reinforcement of the AZ31 by 0.1 wt % INT-WS₂, assuming the diameter of the nanoparticles is 100 nm. Percentage of Value strengthening Symbol Description [MPa] contribution Δσ_(Hall-Petch) enhancement of composite 6.4698 14.4% strength due to grain refining Δσ_(CTE) enhancement of composite 31.2113 69.7% strength due to dislocation density increase Δσ_(Orowan) enhancement of composite 7.0407 15.7% strength due to Orowan strengthening Δσ_(load) enhancement of composite 0.09834 0.2% strength due to load bearing

It is clear from the calculations that the greatest contribution for the reinforcement effect is the increase in the dislocations density at the nanotube-Mg-alloy matrix due to the large mismatch in the thermal expansion of the two materials. In contrast to the Hall-Petch mechanism this effect is more local and is limited to the grain boundaries in the vicinity of the nanotube-metal interface. These calculations were not particularly sensitive to the size of the nanoparticles (e.g. 20-100 nm). However, models taking into account the large anisotropy of the nanotubes would be highly warranted in this case. Further research is required to optimize the process and elucidate the mechanism of the reinforcement effect—in particular using advanced electron microscopy techniques.

Analysis of the contribution of each of the four models to the improved mechanical properties of the Mg-MMC's with different concentration of WS₂ nanotubes is detailed herein below:

Model 1: Hall-Petch Strengthening

Δσ_(Hall-Petch) =K _(y)(d _(m) ^(−1/2) −d _(c) ^(−1/2))

Model 2: Coefficient of Thermal Expansion Difference Effect

${\Delta\sigma}_{CTE} = {\sqrt{3}\beta \; G_{m}b\sqrt{\frac{12{V_{p}\left( {\alpha_{m} - \alpha_{p}} \right)}\left( {T_{process} - T_{test}} \right)}{\left( {1 - V_{P}} \right){bd}_{p}}}}$

Model 3: Orowan Strengthening

${\Delta\sigma}_{Orowan} = {\frac{0.13G_{m}b}{d_{p}\left\lbrack {\left( \frac{1}{2V_{p}} \right)^{1/3} - 1} \right\rbrack}\ln \frac{d_{p}}{2b}}$

Model 4: Load Bearing Effect

Δσ_(load)=0.5V _(p)σ_(ym)

1. AZ31-0.1 wt % (WS₂)

TABLE 3 Parameter for calculation Parameter Description Value Reference/note α_(m) coefficient of thermal expansion of 27.9 × 10⁻⁶° C.⁻¹ Mg alloys-design, the matrix processing and properties F. Czerwinski 2011 α_(p) coefficient of thermal expansion of 15.96 × 10⁻⁶° C.⁻¹ RSC Adv. 2015, 5, the nanoparticles 18391-18400 β dislocation strengthening coefficient 1.25   Acta Materialia 2007, 55, 5115-5121 b magnitude of the burgers vector 0.32 nm Mat. Sci. Eng. A 2008, 483-484, 148-152 d_(c) average grain size in the composite 82.7 μm experimentally sample determined d_(m) average grain size in the monolithic 227.9 μm experimentally sample determined d_(p) nanoparticle diameter 100 nm manufacture supplied average particle size G_(m) shear modulus of the matrix 16.7 GPa calculation and experimentally determined k_(y) Hall-Petch material constant 0.0145 MPa{square root over (m)} calculation and experimentally determined T_(process) processing temperature 720° C. — T_(test) testing temperature 25° C. — V_(p) volume fraction of nanoparticles 0.000023 calculated from weight fraction σ_(ym) Yield stress of the matrix 84.3 MPa experimentally determined

TABLE 4 Calculated contributions of the different mechanisms for the reinforcement of the AZ31 by 0.1 wt % INT-WS₂. Percentage of Value strengthening Symbol Description [MPa] contribution Δσ_(Hall-Petch) enhancement of composite 0.6634 13.1% strength due to grain refining Δσ_(CTE) enhancement of composite 3.0954 61.1% strength due to dislocation density increase Δσ_(Orowan) enhancement of composite 1.3041 25.8% strength due to Orowan strengthening Δσ_(load) enhancement of composite 0.0001 0.0% strength due to load bearing

2. AZ31-0.5 wt % (WS₂)

TABLE 5 Parameter for calculation Parameter Description Value Reference/note d_(c) average grain size in the 136.9 μm experimentally composite sample determined d_(m) average grain size in the 227.9 μm experimentally monolithic sample determined d_(p) nanoparticle diameter 100 nm manufacture supplied average particle size V_(p) volume fraction of 0.001162 calculated from weight nanoparticles fraction

TABLE 6 Calculated contributions of the different mechanisms for the reinforcement of the AZ31 by 0.5 wt % INT-WS₂. Percentage of Value strengthening Symbol Description [MPa] contribution Δσ_(Hall-Petch) enhancement of composite 5.1333 15.8% strength due to grain refining Δσ_(CTE) enhancement of composite 22.0142 67.6% strength due to dislocation density increase Δσ_(Orowan) enhancement of composite 5.3581 16.4% strength due to Orowan strengthening Δσ_(load) enhancement of composite 0.0490 0.2% strength due to load bearing

3. AZ31-1 wt % (WS₂)

TABLE 7 Parameter for calculation Parameter Description Value Reference/note d_(c) average grain size in 77.2 μm experimentally the composite sample determined d_(m) average grain size in 227.9 μm experimentally the monolithic sample determined d_(p) nanoparticle diameter 100 nm manufacture supplied average particle size V_(p) volume fraction of 0.002333 calculated from weight nanoparticles fraction σ_(ym) Yield stress of the 84.3 MPa experimentally matrix determined

TABLE 8 Calculated contributions of the different mechanisms for the reinforcement of the AZ31 by 1 wt % INT-WS₂. Percentage of Value strengthening Symbol Description [MPa] contribution Δσ_(Hall-Petch) enhancement of composite 6.4698 14.4% strength due to grain refining Δσ_(CTE) enhancement of composite 31.2113 69.7% strength due to dislocation density increase Δσ_(Orowan) enhancement of composite 7.0407 15.7% strength due to Orowan strengthening Δσ_(load) enhancement of composite 0.09834 0.2% strength due to load bearing

In one embodiment, this invention provides a method for producing a metal-alloy composite comprising:

-   -   metal alloy; and     -   layered inorganic nanostructures;         wherein said method comprises:     -   heating a metal alloy to form a metal solution;     -   adding a layered inorganic nanostructure into the metal         solution;     -   cooling down the metal solution containing the metal alloy and         the layered inorganic nanostructures to form a composite         material; and     -   optionally performing a solid solution treatment to the         composite material.

FIG. 8 illustrates embodiments of this method. FIG. 8 is a flow chart of a method 800 for making a metal alloy composite material, the method comprises gravity casting. Additional operations may be provided before, during, and after the steps shown in the figure for this method, and some of the operations shown for the method can be eliminated or replaced for additional embodiments of the method. The material of the metal alloy composite and the method for making the same are described in the following with reference to FIG. 9.

The method 800 includes the following steps: a metal alloy matrix is placed in a container (step 801); the metal alloy matrix is heated up to a first temperature and a protective gas is introduced into the container (step 804); the metal alloy matrix is heated up to a second temperature (step 806); the metal alloy matrix is heated up to a third temperature and introducing the protective gas into the container is stopped (step 808); a reinforcement is added into the container and is stirred with the metal alloy matrix to form a mixing slurry (step 810); the mixing slurry is cooled down to form a composite material (step 812); and a solid solution treatment to the composite material is performed (step 814). The detail information related to each of these steps will be described later.

Gravity casting is commonly used as a general casting process in manufacturing and is applicable to methods of this invention as disclosed herein. However, in methods of this invention, other casting methods can be used as known in the art. For example, die casting, vacuum casting etc. can be used.

In some embodiments, the three-step heating process is advantageous as the holding time in each temperature assists in the process. According to this aspect and in one embodiment, heating to only one temperature instead of a three-step heating to three different temperature ranges is not preferred because of the lack of holding time.

In other embodiments however, continuous heating may be used instead of a three-step heating process. However, such heating process consumes more energy and may cost more due to the expensive protection gas used. Other modifications of the heating process are possible in embodiments of this invention, including but not limited to less or more heating steps, modified heating rates, other selected temperatures at each step, and various holding times at each temperature. Any other modifications of the heating process are possible with embodiments of this invention as known in the art.

In some embodiments, the protective gases used are as follows: the first protective gas is Ar (cheaper, exhibiting general protection only at lower temp. say less than 400° C.). The second protective gas is a mixture of SF₆+CO₂ (more expensive, exhibiting much effective protection for Mg at any temperature). However, other gases, mixtures thereof and combinations thereof can be used in methods of this invention as protective gases.

In one embodiment, the protective gas is removed prior to, during or immediately after introduction of the reinforcement material. In other embodiments, the protective gas is kept during or following the introduction of the reinforcement material. However, reinforcement materials might be blown away by the protective gas and/or may react with the SF₆/CO₂ gas mixture in one embodiment.

An embodiment of a furnace as used in the method 800 for making the metal alloy composite is shown in FIG. 9, wherein the container mainly includes a resistance-type furnace 4, an external first gas tank 5, an external second gas tank 8, and a mold 9 under the resistance type furnace 4. Other elements such as a stirring unit 6 and a heating unit 41 will be described herein below.

The method 800 starts from step 801 by placing a metal alloy matrix 1 in a container 3. The container 3 is made of high temperature material, for example, 310S stainless steel or high temperature ceramics, or any suitable material. In the embodiment, the container 3 is a 310S stainless steel crucible. The metal alloy matrix 1 can be any pure metal, metal alloy, or metal/nonmetal composite material. The metal alloy matrix 1 may include a metal (i.e. Mg, Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn, Ag, and Au) and/or a nonmetal (i.e. C, Si) or other suitable materials/compounds. In some embodiments, the metal alloy matrix 1, or called Mg-based alloy, is a metal alloy mainly composed of Mg, such as Mg alloy or Mg—Al alloy (i.e. AZ series like AZ31, AZ61, and AZ80). In other embodiments, the metal alloy matrix 1, or called Al-based alloy, is a metal alloy mainly composed of Al, such as Al alloy or Al—Mg alloy. In an embodiment, the metal alloy matrix 1 is a Mg-based metal alloy including AZ31 and AZ61 Mg alloy. Therefore, the metal alloy composite material formed by the method of the present invention from the Mg-based alloy is Mg-based composite material. In other embodiments, the metal alloy composite material formed by the method of the present invention from the Al-based alloy is Al-based composite material. Reference is now made to Table 9 and Table 10 below. Table 9 shows the compositions of the AZ31 Mg alloy and Table 2 shows the compositions of the AZ61 Mg alloy.

TABLE 9 the compositions of the AZ31 Mg alloy. Element Al Mn Zn Fe Si Cu Ni Mg Weight 3.08 0.393 0.908 0.001 0.022 0.0017 0.0006 balanced Percentage (%)

TABLE 10 the compositions of the AZ61 Mg alloy. Element Al Mn Zn Fe Si Cu Ni Mg Weight 6.5 0.15 0.85 0.07 0.3 0.07 0.009 balanced Percentage (%)

As shown in Table 9 and in Table 10, Mg is the major element in AZ31 Mg alloy and in AZ61 Mg alloy and other elements such as Al, Mn, Zn, Fe, Si, Cu, Ni, are doped into the AZ31 Mg alloy and into the AZ61 Mg alloy. The content of Mg is balanced according to other doping elements.

The method 800 proceeds to step 804 by heating the metal alloy matrix up to a first temperature and introducing a protective gas. In this step, the container 3 is first placed in the resistance-type furnace 4 and the container 3 and the metal alloy matrix 1 in the container 3 are heated by a heating unit 41. At this time, the metal alloy matrix 1 melts with increasing temperature. The first temperature is between 350° C. and 500° C. In the embodiment shown, the first temperature is 400° C. Furthermore, in the progress of heating the metal alloy matrix to the first temperature, the first protective gas is introduced through the first gas vessel (or gas tube) 51 from the external first gas tank 5 when the temperature is raised to a degree between 250° C. and 300° C. to prevent the metal alloy matrix 1 from contacting with air and prevention of the oxidation reaction there between from occurring. The first protective gas may include Ar, Ne, N₂, fluoride, CO₂, a combination thereof, or other suitable gases. In an embodiment, the first protective gas is Ar. Furthermore, the temperature at which the first protective gas is introduced can be adjusted according to the material of the metal alloy matrix 1. In another embodiment, the protective gas is introduced at a temperature between room temperature and the first temperature.

When the temperature is raised to the first temperature, the second protective gas is introduced through the second gas vessel (or gas tube) 81 from the external second gas tank 8 to prevent the metal alloy matrix 1 from contacting air and preventing the combustion reaction there between from occurring. Meanwhile, the introduction of the first protective gas is stopped. The second protective gas may include Ar, Ne, N₂, fluoride, CO₂, a combination thereof, or other suitable gases. In the embodiment, the second protective gas is a gas mixture of CO₂ and SF₆. Moreover, the next step is performed after the temperature is held for 1 min to 2 hours when the first temperature is reached. In a specific embodiment, the holding time under the first temperature is between 10 mins and 15 mins.

The aforementioned first protective gas and the second protective gas can be chosen according to real requirements and the material of the metal alloy matrix 1. In an embodiment, since the metal alloy matrix 1 is Mg alloy or Mg—Al alloy, the protective gas can be a gas mixture of CO₂ and fluoride. Although Mg alloy under CO₂ atmosphere and at various temperatures has a very low oxidation rate, Mg alloy or Mg—Al alloy may still have combustion reaction with increasing temperature. Moreover, when CO₂ includes a mixture of air and moisture, the protective ability of CO₂ decreases. Therefore, the protective gas in such embodiment, besides CO₂, further includes fluoride.

In various fluoride gases, the SF₆ is increasingly used in melting Mg alloy to prevent the combustion of Mg alloy liquid. In room temperature, SF₆ is highly stable. At high temperature, after SF₆ undergoes a chemical reaction with Mg alloy or Mg—Al alloy, a protective layer is formed on the surface of the Mg alloy or Mg—Al alloy. Therefore, SF₆ has an ability of preventing the combustion reaction of Mg alloy liquid from occurring. So, introducing protective gas can prevent the metal alloy matrix 1 from contacting air and the combustion from occurring during heating the metal alloy matrix 1. Moreover, introducing the first or the second protective gas can provide a stirring function by means of gas vibration.

The method 800 proceeds to step 806 by heating the metal alloy matrix up to a second temperature. In this step, the temperature raised from the first temperature to the second temperature allows the metal alloy matrix 1 melting into a metal solution more homogeneously. The second temperature is between 450° C. and 700° C. In the embodiment, the second temperature is 600° C. As mentioned before, the next step is performed after the temperature is held for 1 min to 2 hours when the second temperature is reached. In a specific embodiment, the holding time under the second temperature is between 10 mins and 15 mins.

The method 800 proceeds to step 808 by heating the metal alloy matrix up to a third temperature and stopping introducing the protective gas. In this step, temperature is increased from the second temperature to the third temperature in order to form a metal solution 2 with higher homogeneity. The third temperature is between 600° C. and 800° C. In an embodiment, the third temperature is 730° C. As mentioned before, the temperature is held at the third temperature for 1 min to 2 hour before proceeding to the next step. In the specific embodiment, the temperature is held at the third temperature for 10 min to 15 min. Then, introducing the first protective gas and the second protective gas into the container is stopped, for the subsequent step of adding the reinforcement into the container. That is to say, in the embodiment, after holding temperature at the third temperature (730° C.) for 10 min to 15 min and stopping introducing the first protective gas and the second protective gas, the next step of adding the reinforcement into the metal solution 2 is then performed, which will be discussed later. In another embodiment, the first protective atmosphere and/or the second protective atmosphere is still introduced into the container after increasing temperature to the third temperature.

The method 800 proceeds to step 810 by adding the reinforcement (not shown) into the container 3 and stirring them to form a mixing slurry (not shown). After holding the temperature for 10 mins to 15 mins and stopping introducing the second protective gas when the third temperature (730° C.) is reached, the sealing cap 31 of the container 3 is opened for adding the reinforcement. The reinforcement can be chosen and adjusted properly according to real requirements and the material of the metal alloy matrix 1. In an embodiment, the reinforcement is sulfur-containing compound such as WS₂, MoS₂, or a combination thereof. Furthermore, the shape of the reinforcement may include but not limited to tubular, sheet, bulk, ball, or a combination thereof. The adding content of the reinforcement is between 0.001 wt % and 15 wt %. In the embodiment, the reinforcement used was nano-tubular WS₂, and the adding content thereof was between 0.1 wt % and 0.2 wt %. These materials have been used in embodiments of the processes of this invention. The WS₂ were synthesized according to previously described procedures. However, the present disclosure is not limited the aforementioned descriptions, for example, the material, shape, and the adding content of the reinforcement added into the metal alloy matrix 1 can be adjusted according to real requirements. It should be noted that, in this embodiment, the WS₂ reinforcement will form a strengthen phase, i.e. 2H-phase (2H WS₂ nanotubes) having different phase structure from the metal alloy matrix in the following heat treatment which will be discussed herein below. In another embodiment, the WS₂ reinforcement will form a strengthen phase, i.e. 1T-phase, after the heat treatment. Furthermore, the timing at which the reinforcement is added is after the metal alloy matrix 1 melts into the metal solution 2, the temperature is held at 730° C. for 10 mins to 15 mins, and the second protective gas is stopped being introduced. Therefore, the reinforcement can distribute more homogeneously in the metal solution 2 so that the mechanical properties of the metal alloy composite material are better.

After adding the reinforcement into the metal solution 2, a stirring unit 6 is used to stir the metal solution 2 to homogeneously mix the metal solution and the reinforcement to form homogeneous mixed slurry. The stirring unit 6 may include a motor 61 and stirring blades 62. To be more precise, in the embodiment, the motor 61 is disposed over the sealing cap 31 of the container 3. There are two variable-speed motors 61 over the sealing cap 31. The motor 61 may include but not limited to continuous variable-speed motor. The stirring blades 62 can be disposed with a tilted angle of 45° towards different directions, and each stirring rod has two sets of stirring blades 62 disposed in the metal solution 2. When the stirring blade 62 stirs the metal solution 2, it also stirs the reinforcement having higher density and deposited at the bottom of the container 3. Therefore, the reinforcement and the metal solution 2 can be homogeneously mixed into the mixing slurry through the stirring unit 6. In general, the motor 61 stirs at a stirring rate between about 300 RPM and about 470 RPM and for about 1 min to about 5 mins. In the embodiment, the motor stirs at a stirring rate of about 300 RPM and for about 1 min. Furthermore, in another embodiment, the first protective gas and/or the second protective gas is/are still introduced when stirring the metal solution 2 and the reinforcement. Other stirring systems and devices may be used in embodiments of this invention as known in the art.

The method 800 proceeds to step 812 by pouring the mixing slurry into the mold 9 and leave it to be cooled to form a composite material (not shown). Since the mold 9 is isolated from and under the container 3, the mold 9 can be pre-heated by the heating unit 42 before pouring the mixing slurry into the mold 9 for decreasing the temperature difference between the mold 9 and the mixing slurry to avoid drawbacks such as inhomogeneity caused by the rapid cooling rate. Furthermore, the first protective gas and/or the second protective gas may be introduced through the first gas vessel 52 and/or the second gas vessel 82 before pouring the mixing slurry into the mold 9 to prevent the contact and reaction between air and the mixing slurry. After the stirring is finished, the plug is pull up to open the nozzle 7 at the bottom of the container 3, and the first protective gas and/or the second protective gas are/is introduced through the first gas vessel 52 and the second gas vessel 82 to isolate the mixing slurry from air. At the same time, the mixing slurry flows down into the mold 9 along the nozzle 7, cools and forms the composite material, or so called ingot.

The method 800 proceeds to step 814 by performing a T4 solid solution treatment to the composite material. The T4 represents that solid solution treatment and the natural aging process were performed to a stable state. The solid solution treatment is aimed to make the sample more homogeneous and reduce stress. Ingot cooled down from high temperature in casting process and solid solution process generates residual stress. The residual stress is eliminated by heating the ingot to a temperature at which the yield stress is lower than the residual stress. The composite material in the present disclosure has more defects in the bottom and the top shrink head, and the grain structure in the middle portion is better. Therefore, the specimens used for the following property tests such as stretching test, metallographic analysis, hardness test, and X-ray analysis, are taken from the middle portion of the ingot.

In the embodiment, a heat treatment furnace (not shown) is used to perform a solid solution (heat) treatment to the composite material. The heat treatment is usually performed by raising temperature with a fixed heating gradient to a pre-determined temperature, and followed by keeping the temperature for a while, then raising the temperature and holding the temperature for a longer time again. The heating condition is according to the design of the furnace. For example, the heating gradient can be 5° C./min, from the initial temperature to a temperature between 260° C. and 270° C. and the temperature is held for an hour to release the residual stress in the composite material. Then, the temperature is slowly increased at a heating gradient of 1° C./min and takes 2 hours and 20 minutes to reach a temperature of 400° C. to 450° C. and lasting for 10 hours. Then, the composite material is quenched by e.g. water. In some embodiments, the temperature of the solid solution treatment ranges from about 400° C. to about 600° C. In some embodiments, the composite material is quenched by oil. In some embodiments of the present invention, a solid solution treatment is performed to the composite material for good ductility.

In some embodiments, the oil used for quenching is selected from the following:

1. Straight oils are non-emulsifiable products used in machining operations in an undiluted form. They are composed of base mineral or petroleum oils, and often contain polar lubricants like fats, vegetable oils, and esters, as well as extreme pressure additives such as chlorine, sulfur, and phosphorus. Straight oils provide the best lubrication and the poorest cooling characteristics among the quenching fluids. They are also generally the most economical.

2. Water soluble and emulsion fluids are highly diluted oils, also known as high-water content fluids (HWCF). Soluble oil fluids form an emulsion when mixed with water. The concentrate consists of a base mineral oil and emulsifiers to help produce a stable emulsion. These fluids are used in a diluted form with concentrations ranging from 3% to 10%, and provide good lubrication and heat transfer performance. They are used widely in industry and are the least expensive among all quenching fluids. Water-soluble fluids are used as water-oil emulsions or oil-water emulsions. Water-in-oil emulsions have a continuous phase of oil, and superior lubricating and friction reduction qualities (i.e. metal forming and drawing). Oil-water emulsions consist of droplets of oil in a continuous water phase and have better cooling characteristics (i.e. metal cutting fluids and grinding coolants).

3. Synthetic or semi-synthetic fluids or greases are based on synthetic compounds like silicone, polyglycol, esters, diesters, chlorofluorocarbons (CFCs), and mixtures of synthetic fluids and water. Synthetic fluids tend to have the highest fire resistance and cost. They contain no petroleum or mineral oil base, but are instead formulated from organic and inorganic alkaline compounds with additives for corrosion inhibition. Synthetic fluids are generally used in a diluted form with concentrations ranging from 3% to 10%. They often provide the best cooling performance among all heat treatment fluids. Some synthetics, such as phosphate esters, react or dissolve paint, pipe thread compounds, and electrical insulation. Semi-synthetic fluids are essentially a combination of synthetic and soluble petroleum or mineral oil fluids. The characteristics, cost, and heat transfer performance of semi-synthetic fluids fall between those of synthetic and soluble oil fluids.

4. Micro-dispersion oils contain a dispersion of solid lubricant particles such as PTFE (Teflon®), graphite, and molybdenum disulfide or boron nitride in a mineral, petroleum, or synthetic oil base. Teflon® is a registered trademark of DuPont.

In some embodiments, the oil used for quenching is held at room temperature. Other oil temperatures are suitable for the quenching process as known in the art. In some embodiments, alternative quenching conditions are used. For example and in one embodiment, quenching can be conducted in still air, using air blast, in water at 60-90 degree C. (e.g. for Mg alloy QE22A), or in 30% glycol at room temperature.

Uses of Composites of the Invention

In one embodiment, metal alloy composites of this invention are used in the “4C” industry (Computer, Communications, Consumer Electronics and Car) and for the aerospace industry. In one embodiment, metal alloy composites of this invention are used in medical devices (such as consumable (biodegradable) medical implants), are used for construction, for military devices and systems, for sports and recreation devices and apparatuses etc. In one embodiment, composite materials of this invention are used for ship (marine) construction, for bicycle manufacturing, wheelchair construction, food packaging, etc.

Definitions

The term “nanomaterial” refers to matter or material having at least one dimension in the nanometric range. Within the context of the present invention, a nanomaterial is meant to have at least one dimension being of up to 500 nm. Namely, when the nanomaterial is of particulate form, the average diameter of the particles is up to 500 nm; in other cases, when the nanomaterial is, for example, a nanotube, the diameter of the nanotubes is up to 500 nm. In one embodiment, inorganic layered structures of this invention are inorganic layered nanostructures. Inorganic layered nano structured materials are nano materials. In one embodiment, the layered nano structures of this invention are nanomaterials.

The term layered nanostructure is meant to encompass a structure comprising at least one layer, having at least one dimension in the nanometric range (typically having a thickness of between 0.1 and 250 nm or between 0.1 and 100 nm or between 0.1 and 10 nm). Such nanostructure may be, by some embodiments, selected from a sheet, a distorted sheet, a nano-platelet, a spherical or quasi-spherical nanoparticle, or a tubular nanostructure (e.g. nanotube, nanoscroll). Nanoplatelets are made of 1-50 layers of an inorganic layered nanostructure (e.g. MoS₂ nanoplatelet) which resemble a deck of cards. The nano-platelets can be up to a few microns wide and have thickness of up to 100 nm. In one embodiment, the nano-platelet comprises a flat or slightly curved or moderately curved structure comprising a stack of layers.

In some embodiments wherein the nanomaterial, or the layered nano structure, is in the form of a substantially two-dimensional sheet, the layers may be stacked along a direction perpendicular to surface of the structure. While the atoms within each layer are held by strong chemical bonds, weak van der Waals and/or charge transfer interactions hold the first and second layers together. The term distorted sheet refers, within the context of the present disclosure, to a sheet having at least one portion which is curved (i.e. concaved or convexed) or folded.

In some embodiments where the layered nanostructure is a tubular nanostructure, the nano structure may be a nanotube and/or a nanoscroll.

The term nanotube denotes an elongated tubular structure composed of discrete closed layer(s), i.e. each layer is substantially devoid of dangling, edge bonding sites. Such nanotubes may be selected in a non-limited fashion from single-walled nanotubes, multi-walled nanotubes, double-walled nanotubes, few-walled nanotubes, etc.

In one embodiment, single-walled nanotube means a nanotube comprising a single layer of e.g. WS₂.

The term nanoscroll refers to a single, continuous sheet, which is rolled onto itself to form a tubular structure. The sheet may be rolled once, twice or a plurality of times about a longitudinal axis of the nanoscroll, thereby forming a single, double or multi-walled nanoscroll, respectively. Therefore, a nanoscroll of the invention may be formed out of a continuous sheet having, for example, a single-walled or a multi-walled layered structure.

In some embodiments, the diameter of the tubular nanostructures of the invention is between about 20 and about 500 nm. In some embodiments, the diameter of the tubular nanostructure is between 0.1 nm and 500 nm, between 1 nm and 500 nm, 1 nm and 100 nm, 10 nm and 500 nm, 10 nm and 100 nm, 20 and 450 nm, between 20 and 400 nm, between 20 and 350 nm, between 20 and 300 nm, between 20 and 250 nm, between 20 and 200 nm, between 20 and 150 nm, or even between 20 and 100 nm. In some embodiments, the diameter of the tubular nano structure is between about 25 and about 500 nm, between about 50 and about 500 nm, between about 100 and about 500 nm, between about 150 and about 500 nm, between about 200 and about 500 nm, between about 250 and about 500 nm, or even between about 300 and about 500 nm. In additional embodiment, the diameter of the tubular nanostructure is between about 25 and about 400 nm, between about 50 and about 350 nm, or between about 100 and about 250 nm.

In one embodiment, the diameter ranges mentioned herein above are also applicable to spherical or quasi-spherical layered inorganic nanoparticles.

In one embodiment, composites of this invention and methods of producing thereof are not restricted to metal-alloy composites comprising the inorganic layered nanostructures. Composites of this invention may also comprise pure metals reinforced by the inorganic layered nano structures, wherein the metal-composites are formed similarly to the metal-alloy composites as described herein above. According to this aspect and in one embodiment, the composites comprise one metal and at least one inorganic layered nanostructure. The amount of the inorganic layered nano structure in the metal composite is much smaller than the amount of the metal according to such embodiments. According to this aspect and in one embodiment, the composites consist of one metal and at least one inorganic layered nanostructure. The amount of the inorganic layered nanostructure in the metal composite is much smaller than the amount of the metal according to such embodiments.

In the metal-composites described herein above, some metal impurities may be unintentionally present. Such impurities do not affect the properties of the metal-composites in one embodiment.

Moreover, non-metallic solid materials may be reinforced by inorganic layered nano structures of this invention. Such reinforced materials may include glasses and alumina-based materials.

The term quenching refers to rapid cooling of the material as known in the art. In one embodiment, the material that was kept at an elevated temperature is rapidly cooled by e.g. inserting/placing or dropping the material in/into a liquid possessing a lower temperature. The temperature of the liquid is usually much lower than the temperature of the material thus effectively and rapidly cooling the material.

Gravity casting (GC) comprises casting using gravity to fill (e.g. slurry into) the mold.

The term reinforcement refers to the inorganic layered nanostructured material. The term reinforcement is interchangeable with the term inorganic layered nanostructured material. This term is used in order to emphasize the reinforcement effect of the inorganic layered nanostructured material on the metal or on the metal-alloy to which it is added in processes of this invention.

MWCNT refers to multiwall carbon nanotubes.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.

In one embodiment, the term “a” or “one” or “an” refers to at least one. In one embodiment the phrase “two or more” may be of any denomination, which will suit a particular purpose. In one embodiment, “about” or “approximately” may comprise a deviance from the indicated term of +1%, or in some embodiments, −1%, or in some embodiments, ±2.5%, or in some embodiments, ±5%, or in some embodiments, ±7.5%, or in some embodiments, ±10%, or in some embodiments, ±15%, or in some embodiments, ±20%, or in some embodiments, ±25%.

EXAMPLES Example 1 Materials

The Mg-alloy used for this example was AZ31 with ˜3.0 at % aluminum—available commercially (Taiwan Mach Technology (LINYI) Co.). The chemical composition of the alloy cited by the manufacturer is presented in Table 11.

TABLE 11 Chemical composition (in wt %) of the AZ31 alloy (Mg is about 94.5 wt %). Elements Al Zn Mn Si Fe Cu Ni Mg wt % 3.08 0.908 0.393 0.022 0.001 0.002 0.01 Balance

The WS₂ nanotubes were produced by the reaction of slightly reduced WO₃ nanoparticles with H₂S at temperatures between 850-900° C. using a fluidized bed reactor, (i.e. a vertical reactor where the reacting powder is fluidized (levitated) by a streaming upwards of gas, such as nitrogen, in addition to the reactive gasses, i.e. H₂S and H₂).

Example 2 Preparation of Mg MMC Comprising Inorganic Nanotube

The AZ31 and the WS₂ nanotubes were placed inside a graphite crucible and heated to 400° C. in a resistance-heating furnace for 15 minutes; then a stirring vane was applied; meanwhile, CO₂ and SF₆ gasses were bubbled into the crucible to help mixing the melt. The CO₂ and the SF₆ gasses were also helpful in preventing oxidation of the melt by residual water and air. After that, the melt was heated up to 600° C. for 15 minutes. The crucible was further heated gradually up to 700-720° C., with the molten alloy being stirred with a vane operated at 350 rev/min for 3 minutes. Finally, the composite melt was poured into a metallic mold. The Mg MMCs containing nanotubes with weight fraction of 0.1-1 wt % (see Table 12) were now ready for further mechanical testing. Each composition was repeated at least three times. Initially, blade stifling (“a” in Table 12) was used for mixing the nanotubes in the metal melt. However, due to the small size of the crucible, the blade propeller led to vortices and non-uniform mixing of the nanotubes in the Mg MMC. Therefore in the later preparations, the blade stirrer was replaced by a rod stirrer (“b” in Table 12).

TABLE 12 Specimens used for this study and their notation (*x indicates the No. of the specimen with the same material constituent). wt % of Blade (a) or rod (b) Notation Matrix INT-WS₂ stirring AZ31-x* AZ31 0 x = 1&2 (a); 3&4 (b) AZ31INT0.1-x AZ31 0.1 x = 1-3 (a) AZ31INT0.5-x AZ31 0.5 x = 1-3 (b) AZ31INT1-x AZ31 1 x = 1-3 (b)

To accommodate for the relatively small amounts of available WS₂ nanotubes (in total less than 20 g), the melt-stirring reactor was modified in the present example. A schematic rendering of the reactor with the gas supply lines is shown in FIG. 2A. FIG. 2B shows a schematic view of the stainless steel crucible used for melting of the AZ31 alloy. To minimize the amount of the nanotubes used and allow larger number of samples to be prepared and tested, the container of the melt was modified so that ingot sizes of app. 100 g could be fabricated. A picture of a few ingots obtained after the melt stirring at different temperatures is shown in FIG. 2C. Noticeably, the ingots which were prepared at temperatures of 700° C. and above looked more uniform compared to those prepared at lower temperatures. One major challenge for this study was the need to protect the reactive mixture, and especially the nanotubes, against high-temperature oxidation.

Example 3 Analysis of Mg MMC Comprising Inorganic Nanotube

A vertical theta-theta diffractometer (TTRAX III, Rigaku, Japan) equipped with a rotating Cu anode operating at 50 kV and 240 mA was used for XRD studies. The following electron microscopes were used in this work: SEM model LEO model Supra, 7426. The SEM was equipped with EDS system model Oxford INCA. TEM (Philips CM120 TEM) operating at 120 kV was equipped with an EDS detector (EDAX-Phoenix Microanalyzer). For electron microscopy and analysis, the collected powder was sonicated in ethanol and placed on a carbon-coated Cu grid (for TEM).

For the mechanical testing, an MTS Model 458 axial/torsional testing systems was used according to standard ASTM B 557M-02a (Standard Test Methods of Tension Testing Wrought and Cast Aluminum- and Magnesium-Alloy Products).

For analysis, samples (5×5×3 mm³) were cut from the top, middle and bottom of the ingot. Minute oxidation of the top and bottom surfaces was unavoidable, but was limited to the top surface layer of the specimen (few microns), only. X-ray diffraction (XRD) patterns of the prepared MMC (AZ31INT0.5) are shown in FIG. 3. A small reflection peak from the (002) plane of the INT at 13.91° (interlayer spacing of 6.36 Å) is shifted with respect to bulk 2H-WS₂. This downshift represents a 2-3% expansion in the interlayer spacing and is attributed to relaxation of the strain in the nanotubes. This lattice expansion was attributed to strain relaxation of the WS₂ layers in the nanotubes. Furthermore, the slightly larger swelling of the interlayer spacing in the present case could be attributed to Mg intercalation between the WS₂ layers. It is nevertheless not clear if the Mg intercalation occurred within the nanotubes or into portion thereof, which exfoliated during the processing. More careful inspection of some of the XRD patterns reveals two extra peaks at 30° and 35° in the MMC (darker curve). The peak at 30° can be possibly assigned to the compound Al₂CO, which is formed by the high temperature reaction between aluminum and the CO₂.

Scanning electron microscopy (SEM) combined with energy dispersive X-ray spectroscopy (EDS) was carried out for the different MMC samples. The carbon content of the analyzed samples was larger than 10 at % in most cases. This contamination could be attributed to the CO₂ gas used for the high-temperature processing of the MMC in the melt-stirring process. A high-temperature reaction between the magnesium, residual oxygen and the CO₂ gas could lead to the formation of MgCO₃ phase. This deposit could explain the presence of both carbon and oxygen in appreciable amounts in the alloy (mainly on the surface). Oxygen was also present in significant amounts (5-10 at %) and could reflect the great sensitivity of the samples to surface oxidation (MgO). Table 13 shows a typical EDS analysis of a specimen with 0.5 wt % WS₂. The analysis was made over a large surface area of 1×2 mm² thus representing a considerable surface averaging.

TABLE 13 Results of the EDS analysis of sample AZ31INT0.5-2 and AZ31INT0.5-3 (excluding carbon and oxygen). “2” refers to sample 2 (having the same constituents of AZ61, 0.5 wt % INT); “3” refers to sample 3 (having the same constituents of AZ61, 0.5 wt % INT). AZ31INT0.5-2 AZ31INT0.5-3 Element wt % at % wt % at % Mg K 96.15 96.82 94.93 97.33 Al K 3.35 3.04 1.63 1.51 W M 0.58 0.08 0.60 0.08 Zn K 0.20 0.07 0.59 0.22 Si K 0.25 0.22 S K 0.35 0.27 0.02 0.02 Fe K 0.02 0.01 Total 100.00 100.00 100.00 100.00

The EDS analysis showed small non-uniformities in the tungsten content. However, overall the tungsten content was in most cases not far from the value of 0.5 wt % of the added amounts of the nanotubes. However, the sulfur to tungsten atomic ratio was in most cases smaller than the expected one—1:2. The reduced sulfur content in the MMC reflected possibly partial oxidation of the nanotubes during the high-temperature melt-stirring process. It reflected possibly also the limited inaccuracy of the method at such small sulfur concentrations.

Example 4 Mechanical Properties of Mg MMC Comprising Inorganic Nanotubes

Numerous tensile tests were carried out for the AZ31INT samples. FIG. 4 shows a typical result of such tests for the AZ31 alloy filled with 1 wt % INT-WS₂. Two obvious conclusions can be drawn from this figure: 1. there exists some scattering in the data, which therefore necessitated to average over many repetitive measurements. 2. The addition of the nanotubes had relatively minor effect on the stiffness and yield strength of the samples, but had a remarkable advantageous effect on the tensile strength and the strain (elongation) and consequently on the fracture toughness of the MMCs (see Table 14). Notwithstanding the scattering in the data, a reproducible and significant improvement in the fracture toughness of the Mg-MMCs with addition of minute amounts of WS₂ nanotubes was confirmed. FIG. 5 presents a summary of the mechanical properties of the pure alloy and the WS₂ nanotubes-based MMCs after averaging. Indeed, the addition of small amounts of INT-WS₂, with no additional mechanical processing, leads to significant improvements in the mechanical behavior of the Mg-alloy (AZ31). In particular, both the strength and strain of the MMC was ameliorated, which produced a remarkable improvement in its fracture toughness.

TABLE 14 Fracture toughness of the pure AZ31 Mg-alloy and the INT-WS₂ (1 wt %)-Mg-alloy composites. Toughness [MPa] % change AZ31-4 13.1 — AZ31INT1-1 38.1 190 AZ31INT1-2 15.3 17 AZ31INT1-3 48.8 272 AZ31INT1-avg. 34.1 160

Example 5 Metallographic Analysis of Mg MMC Comprising Inorganic Nanotubes

In order to elucidate the reinforcement effect of the nanotubes, metallographic analysis was carried-out for the MMCs. FIG. 6 shows a typical optical micrograph of the surface of three AZ31INT1 samples and pure AZ31 alloy. Visibly the nanotubes-containing MMC possess smaller grains. The results of the grain-size analyses are shown in the block diagrams in FIG. 7A. It is clear from this figure that the addition of small amounts of INT-WS₂ to the Mg-MMCs leads to substantial reduction in their average grain-sizes. Also noticeable is the fact that the average grain size of the different AZ31INT1 samples (AZ31INT1, 1-3) is similar (app. 70 microns). This observation suggests that the nanotubes are uniformly distributed in the Mg-MMC matrix. Finally, metallographic analysis of quite a few MMCs surfaces, with different nanotubes content, is displayed in the block diagram in FIG. 7B. Accordingly, as the nanotubes concentration goes-up the grain size is reduced. This analysis strongly suggests a relationship between the grain-size and the mechanical properties of the MMCs. Seemingly therefore; the nanotubes play the role of nucleation centers which lead to the diminution of the grain size of the MMC during solidification. It is not clear at present time, if the nanotubes are distributed evenly through the bulk of the grain or they segregate to the grain boundaries between the different grains. Remarkably also, the error bars, which are representative of the statistical analysis of the grain size diminish with the addition of increasing amounts of nanotubes to the Mg alloy. This fact suggests that the nanotubes induce much more uniform nucleation of the grains in the Mg-alloy, as compared to the pure one.

Example 6 Formation of Mg MMC Comprising Layered Inorganic Material by Alloy Heating Followed by Addition of Layered Inorganic Structures

In the following description, the AZ31 Mg-based composite material under the T4 solid solution heat treatment is represented as “AZ31-T4,” while the AZ61 Mg-based composite material under the T4 solid solution treatment is represented as “AZ61-T4.”

Reference is now made to FIGS. 10A through 10C and FIGS. 11A through 11C, which respectively illustrates X-ray diffraction patterns of AZ31-T4 and AZ61-T4 and added with none or with 0.2 wt % WS₂. Wherein the middle portion and the bottom portion of the specimen added with 0.2 wt % WS₂ are taken for measurement. Wherein, FIG. 10B and FIG. 10C are a partial enlarged image of FIG. 10A (between angle 36° and 38° and between angles 57° and 58), while FIG. 11B and FIG. 11C are a partial enlarged image of FIG. 11A (between angle 36° and 38° and between angle 63° and 64°). As observed from FIG. 10A, the middle portion of the AZ31-T4 added with 0.2 wt % WS₂ (labeled as “1002”) and the bottom portion of the AZ31-T4 added with 0.2 wt % WS₂ (labeled as “1003”) provide a very weak signal of the WS₂ strengthen phase but a better signal at (101) between 36° and 37°, relatively stronger than other peaks and higher than (1001) of AZ31-T4, which indicates that the crystallinity at (101) is better. Similar phenomena occurs at (1111) of AZ61-T4 in FIG. 11A, the middle portion of the AZ61-T4 added with 0.2 wt % WS₂ (labeled as “1112”), and the bottom portion of the AZ61-T4 added with 0.2 wt % WS₂ (labeled as “1113”). Reference is now made to FIG. 10B and FIG. 11B again, which is an enlarged image of the peak (101) at an angle between 36° and 38° for comparison. It can be observed that the 2-theta value of peak (1001) of AZ31-T4 and peak (1111) of AZ61-T4 after added 0.2 wt % WS₂ increases significantly, as shown in “1002”, “1003”, “1112”, and “1113”, which makes the 2-theta value of the peak shift to the right with a shifting degree of 0.08. Furthermore, as shown in FIG. 10C and in FIG. 11C, the peak in the high angle region (between 57° and 58° in FIG. 10C and between 63° and 64° in FIG. 11C) also shifts to the right with a shifting degree of 0.12, which proves that the solid solution does occur. When solid solution occurs, the Mg atoms in the lattice are replaced by S atoms or W atoms. This causes lattice shrinkage, decreasing the inter-atom distance (i.e. decreasing the distance between crystal planes) that causes inter-reaction between interior dislocations and crew dislocations to enhance the hardness. It should be noticed that, after solid solution treatment, there is still an amount of WS₂ strengthen phase, such as the aforementioned 2H-phase WS₂ strengthen phase, remaining in the metal alloy matrix. By adjusting the temperature and duration of the solid solution treatment, the ratio of the WS₂ strengthen phase not dissolved into the matrix to obtain the ideal mechanical properties and ductility.

Please refer to FIGS. 12A through 12F and FIGS. 13A through 13F, which respectively illustrate the metallographic photos of AZ31 and AZ61 Mg-based composite material added with different weight percentage of the reinforcement before and after the solid solution treatment. It should be noticed that WS₂ reinforcement will form the aforementioned WS₂ strengthen phase in the composite material. Wherein, FIG. 12A, FIG. 12B, and FIG. 12C respectively represents AZ31 Mg-based composite material without solid solution treatment and added with none, 0.1 wt %, and 0.2 wt % WS₂. While FIG. 12D, FIG. 12E, and FIG. 12F respectively represents AZ31 Mg-based composite material with solid solution treatment and added with none, 0.1 wt %, and 0.2 wt % WS₂. Similarly, FIG. 13A, FIG. 13B, and FIG. 13C respectively represents AZ61 Mg-based composite material without solid solution treatment and added with none, 0.1 wt %, and 0.2 wt % WS₂. While FIG. 13D, FIG. 13E, and FIG. 13F respectively represents AZ61 Mg-based composite material with solid solution treatment and added with none, 0.1 wt %, and 0.2 wt % WS₂.

In FIGS. 12A through 12C, there is a β phase (Mg₁₇Al₁₂) of AZ series alloys located at the grain boundary, which will decrease the ductility of the Mg-based composite material. The metallographic photos of Mg-based composite material after solid solution treatment, as shown in FIGS. 12D through 12F, obviously show the shape and size of the grains, and most of the β phase that is dissolved into the grains instead of existing at grain boundary. Similar phenomena occur in AZ61 Mg-based composite material (as shown in FIGS. 13A through 13F), despite that the Al content in AZ61 is higher so that the amount of the β phase is higher than that of AZ31.

The average grain sizes of various Mg-based composite material ingots (AZ31-T4 and AZ61-T4) with different additive amount of the reinforcement are discussed in the following. It should be noticed that WS₂ reinforcement will form the aforementioned strengthening phase of WS₂ in the composite materials. The grain sizes are calculated by linear intercept method and are summarized in Table 15 as shown below.

TABLE 15 average grain sizes of various Mg-based composite materials with different additive amount of WS₂. WS₂ 0 wt % 0.1 wt % 0.2 wt % AZ31-T4 80.0 μm 55.0 μm 40.0 μm AZ61-T4 51.7 μm 37.5 μm 31.8 μm

As evident from Table 15, the average grain size of the AZ31 undergoing the T4 treatment is 80.0 μm. When the AZ31-T4 Mg alloy is added with 0.1 wt % WS₂, the average grain size decreases into 50 μm (37.5% decrease). When further increasing the adding content of WS₂ of the AZ31-T4 Mg alloy up to 0.2 wt %, the average grain size further decreases into 40 μm (50% decrease). On the other hand, the average grain size of the AZ61 undergoing the T4 treatment is 51.7 μm. When the AZ61-T4 Mg alloy is added with 0.1 wt % WS₂, the average grain size decreases into 37.5 μm (27.5% decrease). When further increasing the adding content of WS₂ of the AZ61-T4 Mg alloy up to 0.2 wt %, the average grain size further decreases into 31.8 μm (38.5% decrease). Wherein, since the AZ61 includes higher content of Al, which will restrain the grain growth, the average grain size of the AZ61-T4 is smaller than the AZ-31-T4. Furthermore, adding the reinforcement into the metal alloy matrix, which will forms the aforementioned strengthen phase in the composite material), makes the metal alloy matrix have more nucleation points during the casting process, which will restrain grain growth and forms more smaller grains in a specific volume.

The invention further perform Vickers-hardness test to Mg-base composite material ingots. The Vickers-hardness (HV) of AZ31-T4 and AZ61-T4 composite materials with different additive amount of WS₂ are summarized in Table 16 as shown below.

TABLE 16 Vickers-hardness of various Mg-based composite materials with different additive amount of WS₂. WS₂ 0 wt % 0.1 wt % 0.2 wt % AZ31-T4 51.0 HV 54.3 HV 55.9 HV AZ61-T4 55.4 HV 58.3 HV 58.6 HV

As shown in Table. 16, the hardness of the AZ31-T4 Mg-based composite material without reinforcement is 51.0 HV, while the hardness of the AZ31-T4 Mg-based composite material added with 0.1 wt % WS₂ is 54.3 HV (6.5% increase). When further increasing the adding content of WS₂ of the AZ31-T4 Mg-based composite material up to 0.2 wt %, the hardness further increases to 55.9 HV (9.6% increase). On the other hand, the hardness of the AZ61-T4 Mg-based composite material without reinforcement is 55.4 HV, while the hardness of the AZ61-T4 Mg-based composite material added with 0.1 wt % WS₂ is 58.3 HV (5.2% increase). When further increasing the adding content of WS₂ of the AZ61-T4 Mg-based composite material up to 0.2 wt %, the hardness further increases to 58.6 I-TV (5.8% increase). Since the content of Al in the AZ61-T4 is higher than that of the AZ31-T4, the precipitated brittle β phase in the AZ61-T4 is also higher than that of the AZ31-T4. Thus, the hardness of the AZ61-T4 without reinforcement added is higher than that of the AZ31-T4 without reinforcement added. Moreover, as known from the aforementioned Table 15, adding of the reinforcement such as WS₂ will decrease the grain size and causes grain strengthen effect. Therefore, the hardness of the Mg-based composite material added with 0.2 wt % WS₂ is higher than that of the Mg-based composite material added with 0.1 wt % WS₂.

Besides the aforementioned Vickers-hardness test, the invention further uses a tension test for discussing the influence of additive amount of the reinforcement on mechanical properties of AZ31-T4 and AZ61-T4 Mg-based composite material. After the aforementioned gravity mold casting process and T4 solid solution process, both AZ31-T4 and AZ61-T4 Mg-based composite materials are made into specimens according to ASTM E8-69. Each of the specimens has a gage width (GW) equals to 6 mm, a gage length (GL) equals to 13 mm and a holding length (HL) equals to 12 mm, and the total length of the specimen equals to 45 mm. Then, a tension test is performed on the specimen with a tension speed equals to 1 mm/min by a MTS testing machine. Each group of the Mg-based composite materials is measured 5 times and the average value is calculated. Thus, mechanical properties of different AZ31-T4 and AZ61-T4 composite materials with different additive amount of WS₂ are compared and summarized in Table 17 as shown below.

TABLE 17 mechanism properties of Mg-based composite materials with different additive amount of WS₂. Mg-based Ultimate Tensile composite WS₂ Yield Strength Strength Elongation material (wt %) (MPa) (MPa) (%) AZ31-T4 0 74.8 134.8 13.90 0.1 85.7 171.7 23.42 0.2 87.2 208.2 25.74 AZ61-T4 0 76.8 130.4 10.0 0.1 79.8 157.3 19.08 0.2 85.4 188.7 19.62

As shown in Table 17, the yield strength, the ultimate tensile strength, and the elongation of either the AZ31-T4 or the AZ61-T4 can be increased simultaneously and significantly by adding small amount of WS₂. The yield strength, the ultimate tensile strength, and the elongation of the AZ31-T4 added with 0.2 wt % of WS₂ are 87.2 MPa, 208.2 MPa, and 25.74% respectively. While the yield strength, the ultimate tensile strength, and the elongation of the AZ61-T4 added with 0.2 wt % of WS₂ are 85.4 MPa, 188.7 MPa, and 19.62% respectively. The yield strength, the ultimate tensile strength, and the elongation of the AZ31-T4 increase 40.1%, 15.9%, and 110.0% respectively. While, the yield strength, the ultimate tensile strength, and the elongation of the AZ61-T4 increase 30.1%, 6.0%, and 144.9% respectively. In the aspect of mechanical strengths, since the content of Al in AZ61 is higher than that in AZ31, there is more β phase at grain boundary in AZ61, which decreases the number of initial points of uneven cracks during the stretching test. Therefore, the mechanical strength of AZ31-T4 is higher than that of the AZ61-T4. On the other hand, the reasons of increasing the mechanical strength of the Mg-based composite material after adding the reinforcement are increasing dislocation density, grain refinement, and the loading shift of stress.

In the aspect of the ductility, both AZ31-T4 and AZ61-T4 show an increasing trend after adding the reinforcement. It is because that, after adding the reinforcement into the metal alloy matrix, grain size decreases, WS₂ strengthen phase distributes more homogeneously, and additional nonbasal slip systems are provided, increases ductility. Furthermore, since the AZ31-T4 has less brittle phase, it has higher ductility than that of the AZ61-T4.

The AZ31 and AZ61 Mg-based composite material made through the gravity casting method of the present disclosure and go through T4 solid solution treatment have excellent mechanical properties. After adding the WS₂ reinforcement into the AZ31-T4 and the AZ61-T4, the formed WS₂ strengthen phase makes the hardness, tensile strength, and the elongation improved significantly. The ultimate tensile strength, the yield strength, the elongation, and the hardness of the AZ31-T4 Mg-based composite material added with 0.2 wt % WS₂ are 208.2 MPa, 87.2 MPa, 25.7%, 55.9 HV respectively, which are 54.5%, 16.6%, 85.2%, 9.6%, and 50.0% improved respectively compared with the AZ31-T4 without addition of WS₂. On the other hand, the ultimate tensile strength, the yield strength, the elongation, and the hardness of the AZ61-T4 Mg-based composite material added with 0.2 wt % WS₂ are 188.7 MPa, 85.4 MPa, 19.6%, 58.6 HV respectively, which are 44.7%, 11.2%, 95.4%, 5.8%, and 38.5% improved respectively compared with the AZ61-T4 without addition of WS₂.

While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention. 

What is claimed is:
 1. A metal or a metal-alloy composite comprising: a. metal or a metal alloy; and b. inorganic layered nanostructured material, wherein the inorganic layered nanostructured material does not comprise carbon.
 2. (canceled)
 3. The metal-alloy composite of claim 1, wherein said metal alloy composite comprises Mg, Fe, Cu, Al, Ti, Zn, Ni, Hg, Mn, Ag, Au or a combination thereof.
 4. The metal-alloy composite of claim 3, wherein the base metal in said metal alloy is Mg.
 5. The metal-alloy composite of claim 3, wherein the base metal in said metal alloy is Fe, Cu, Al, Ti, Zn, Ni, Hg.
 6. The metal-alloy composite of claim 1, wherein said metal alloy comprises one or more secondary metals.
 7. The metal-alloy composite of claim 6, wherein said secondary metal(s) in said metal alloy comprises Al, Zn, Mn or a combination thereof.
 8. The metal-alloy composite of claim 6, wherein said secondary metal(s) in said metal alloy comprises Zn, Al, Cu, Mg, Mn, Sn, Sb, Ag, Au, Pt, Pd, In, Zr, Ni, Fe, C, Si, Ti, Pb, Be, Y, Cc, Nd, Ca, Os, As, Ba, B, Cr, Co, Ga, Ge, Li, Rh, Ru, Se, Sr, W, Na, Pt, Cd, Bi, or a combination thereof.
 9. The composite of claim 1, wherein said layered inorganic nanostructured material is a spherical nanoparticle, a quasi-spherical nanoparticle, a nanotube, a nanoscroll, a nano-platelet or a combination thereof.
 10. The composite of claim 1, wherein said inorganic layered nanostructured material comprises WS₂, MoS₂, or a combination thereof.
 11. The metal alloy composite material of claim 9, wherein the sulfur-containing compound is 2H-phase WS₂.
 12. The composite material of claim 1, wherein the concentration of said layered inorganic nanostructured material in said composite ranges between 0.001 wt % to 15 wt %.
 13. The composite of claim 12, wherein the concentration of said layered inorganic nanostructured material in said composite ranges between 0.001 wt % and 1 wt %.
 14. The metal-alloy composite of claim 1, wherein the % increase in fracture toughness of said composite with respect to an alloy without the inorganic layered structure ranges between 250% and 300%.
 15. The metal-alloy composite of claim 1, wherein the % increase in yield strength of said composite with respect to an alloy without the inorganic layered structure ranges between 15% and 20%.
 16. The metal-alloy composite of claim 1, wherein the % increase in ultimate tensile strength of said composite with respect to an alloy without the inorganic layered structure ranges between 45% and 70%.
 17. The metal-alloy composite of claim 1, wherein the elongation of said composite with respect to an alloy without the inorganic layered structure ranges between 140% and 400%.
 18. The metal-alloy composite of claim 1, wherein the size of the grains of said composite ranges between 50 μm-100 μm.
 19. A method for producing a metal or a metal-alloy composite comprising: metal or metal alloy; and layered inorganic nanostructures; wherein said method comprises: a. placing said metal or metal alloy and said inorganic layered nanostructured material in a crucible; b. heating said metal or metal alloy and said inorganic layered nanostructured material in said crucible to a first temperature, forming a melt; c. stirring said melt of said metal or metal alloy and said inorganic layered nanostructured material in said crucible; d. bringing gas into contact with said melt in said crucible; e. optionally heating said melt in said crucible to a second temperature; f. optionally heating said melt in said crucible to a third temperature; g. pouring said melt into a mold; h. cooling said melt; thus forming a solid metal or metal-alloy composite.
 20. (canceled)
 21. The method of claim 19, wherein the order of steps b, c, and d is switched or wherein steps b; c, and d are conducted in parallel or at least partially overlap in time.
 22. The method of claim 19, wherein said first temperature is 380-420° C., said second temperature is 580-620° C. and said third temperature is 680-720° C.
 23. The method of claim 19, wherein said gas is selected from the group consisting of CO₂, SF₆, N₂, Ar or a combination thereof.
 24. The method of claim 19, wherein said melt is kept at said first temperature and optionally at said second temperature and optionally at said third temperature for a period of time ranging between 10 min-20 min.
 25. The method of claim 19, wherein said heating is conducted in a resistance-heating furnace.
 26. The method of claim 19, wherein said stirring is conducted using a stirrer comprising a vane, a blade, a rod, a screw or a combination thereof.
 27. A method for producing a metal or a metal-alloy composite comprising: metal or metal alloy; and layered inorganic nanostructures; wherein said method comprises: heating a metal or a metal alloy to form a melt or a metal solution; adding a layered inorganic nanostructure into the metal or metal solution; cooling down the metal or metal solution containing the metal or metal alloy and the layered inorganic nanostructures to form a composite material; and optionally performing a solid solution treatment to the composite material.
 28. (canceled)
 29. The method of claim 27, wherein the metal alloy is a magnesium-based alloy or an aluminum-based alloy.
 30. The method of claim 27, wherein the layered inorganic nanostructure is a sulfur-containing compound.
 31. The method of claim 30, wherein the sulfur-containing compound comprises tungsten disulfide (WS₂), molybdenum disulfide (MoS₂) or a combination thereof.
 32. The method of claim 27, further comprising introducing a protective gas when heating the metal or the metal alloy.
 33. The method of claim 32, wherein introducing the protective gas comprises introducing helium (He), argon (Ar), nitrogen (N₂), sulfur hexafluoride (SF₆), carbon dioxide (CO₂) or a combination thereof.
 34. The method of claim 32, wherein protective gas introduction is stopped after holding a temperature of between 600° C. and 800° C. for 1 min to 2 hour.
 35. A metal composite or a metal-alloy composite comprising: a. metal or metal alloy; and b. inorganic layered nanostructured material. wherein said metal composite or metal-alloy composite is produced by the method described in claim
 19. 36. A metal composite or a metal-alloy composite comprising: a. metal or metal alloy; and b. inorganic layered nanostructured material. wherein said metal composite or metal-alloy composite is produce by the method described in claim
 27. 